Columbia  ©ntoertfitj 
intIifCttpoflemg0rk 

College  of  ^fjpsiictans!  ano  burgeons 


From  the  Library  of 

PROFESSOR  PHILIP  HANSON  HISS 

1868-1913 

Donated  by 

Mrs.  Philip  Hanson  Hiss 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/textbookofhistol1904bail 


A 

TEXT-BOOK    OF 
HISTOLOGY 


By 

FREDERICK  R.  BAILEY,  A.M.,  M.D. 

Adjunct  Professor  of  Normal  Histology,  College  of  Physicians  and  Surgeons— Medical  Department, 
Columbia  University,  New  York  City 


PROFUSELY    ILLUSTRATED 


NEW     YORK 

WILLIAM    WOOD   &   COMPANY 

MDCCCCIV 


Copyright,  IWi, 
By  WILLIAM   WOOD   AND   COMPANY 


THE    PUBLISHERS'    PRINTING    COMPANY 
NEW    YORK 


PREFACE. 


The  primary  aim  of  the  writer  in  the  preparation  of  these  pages 
has  been  to  give  to  the  student  of  medicine  a  text-book  of  histology 
for  use  in  connection  with  practical  laboratory  instruction,  and  espe- 
cially to  furnish  to  the  instructor  of  histology  a  satisfactory  manual 
for  classroom  teaching.  With  these  objects  in  view,  the  text  has 
been  made  as  concise  as  possible  consistent  with  clearness,  and  the 
writer  has  attempted  to  make  the  more  essential  elements  stand  out 
somewhat  from  the  necessarily  accompanying  details. 

It  has  been  impossible  to  accomplish  this  without  some  sacrifice 
of  uniformity  of  treatment  and  of  logical  sequence.  This  is  espe- 
cially noticeable  in  the  chapter  on  the  nervous  system,  which  has 
been  made  much  fuller  and  more  "practical"  than  is  usual.  The 
author's  reason  for  the  method  of  treatment  there  adopted  and  for  the 
considerable  amount  of  anatomy  which  this  chapter  contains  being 
the  apparent  success  the  method  has  met  with  in  the  teaching  of  this 
always  difficult  subject  to  students. 

The  chapter  on  general  technic  is  intended  to  furnish  the  student 
with  only  the  more  essential  laboratory  methods.  For  special  and 
more  elaborate  methods  the  student  is  referred  to  the  special  works 
on  technic  mentioned  at  the  close  of  the  chapter.  The  special 
technic  given  in  connection  with  the  different  tissues  and  organs  is 
in  most  cases  such  as  can  be  conveniently  used  for  the  preparation 
of  class  sections. 

The  original  illustrations  are  from  drawings  by  Mr.  A.  M.  Miller, 
to  whom  the  writer  is  greatly  indebted  for  his  careful  and  accurate 
work.  The  uselessness  of  redrawing  perfectly  satisfactory  illustra- 
tions has  led  the  writer  to  borrow  freely  from  various  sources,  each 

cut  being  duly  accredited  to  the  work  from  which  it  has  been  taken. 

iii 


iv  PREFACE. 

For  all  of  these  the  author  wishes  to  express  his  appreciation  and 
obligation.  He  is  also  deeply  indebted  to  Dr.  O.  S.  Strong  for  his 
careful  review  and  criticism  of  the  chapter  on  the  nervous  system 
and  for  his  supervision  of  the  drawing  of  Figs.  263  and  264 ;  to  Dr. 
G.  C.  Freeborn,  his  predecessor  as  Instructor  of  Histology  at  the 
College  of  Physicians  and  Surgeons,  for  many  valuable  suggestions ; 
and  to  Dr.  T.  Mitchell  Prudden  for  his  careful  and  critical  review  of 
the  author's  copy. 


CONTENTS. 


PART    I.— HISTOLOGICAL   TECHNIC. 

CHAPTER    I. 

PAGE 

General  Techxic. 

General  Considerations.         ..........  3 

Examination  of  Fresh  Tissues.      .........  3 

Dissociation  of  Tissue  Elements, 4 

Teasing.    .............  4 

Maceration = 4 

Fixation.          .............  4 

Hardening, 7 

Preserving,      .............  7 

Decalcifying. S 

Embedding, 9 

Celloidin  Embedding 9 

Paraffin  Embedding,       .         .         .         .         .        .         .         .        .         .11 

Section  Cutting 12 

Celloidin  Sections.           ...........  12 

Paraffin  Sections,    .         .         .         .         .         .         .        .         .         c        .12 

Staining, .  13 

Nuclear  Dyes, 13 

Plasma  Dyes,  .         .         .         .         .         .        .        .        .        .         -15 

Staining  Sections, 16 

Staining  in  Bulk, 17 

Mounting.        .............  17 

Staining  and  Mounting  Paraffin  Sections, 19 

Injection.         .............  20 


CHAPTER    II. 

Special  Staining  Methods. 

Silver  Nitrate  Method  of  Staining  the  Intercellular  Substance, 
Chlorid  of  Gold  for  Demonstrating  Connective-tissue  Cells. 
Weigert's  Elastic  Tissue  Stain.     ....... 

Golgi"s  Chrome-silver  Method  for  Staining  Secretory  Tubules. 

v 


VI 


CONTENTS. 


Mallory's  Hematoxylin  Stain  for  Connective  Tissue, 

Osmic  Acid  Stain  for  Fat, 

JenneFs  Blood  Stain,     ....... 


24 
24 
24 


CHAPTER    III. 


Special  Neurological  Staining  Methods 
Weigert's  Method  of  Staining  Medullated  N 

Weigert-Pal  Method, 
Golgi  Methods  of  Staining  Nerve  Tissue, 

Slow  Method, 

Rapid  Method, 

Mixed  Method, 

Formalin-bichromate  Method, 

Bichloride  Method, 

Golgi-Cox  Method, 

Nissl's  Method 

General  References  on  Technic,    . 


erve  Fibres, 


PART   II.— THE   CELL. 


CHAPTER   I. 


The  Cell, 

General  Structure, 
Structure  of  a  Typical  Cell,  . 
The  Cell  Body, 
The  Cell  Membrane, 
The  Nucleus,  . 
The  Centrosome,     . 
Vital  Properties  of  Cells, 
Metabolism, 
Function, 
Irritability, 

Motion,     .... 
Amoeboid, 
Protoplasmic,   . 
Ciliary, 
Reproduction, 

Direct  Cell-division, 

Indirect  Cell-division, 

Fertilization  of  the  Ovum,      . 

Technic,  .... 

References   for  further  study, 


33 
33 
34 
35 
35 
36 
37 
37 
37 
37 
38 
38 
38 
38 
39 
39 
39 
42 
46 

47 


CONTENTS. 


vn 


PART   III.— THE   TISSUES. 

CHAPTER    I. 

PAGE 

Histogenesis— Classification 51 

Tissues  Derived  from  Ectoderm, 51 

Tissues  Derived  from  Entoderm, 51 

Tissues  Derived  from  Mesoderm, S2 


CHAPTER    II. 


Epithelium  (Including  Mesothelium 
Histogenesis, 
General  Characteristics, 
Classification, 
Simple  Epithelium, 

Simple  Squamous,  . 

Simple  Columnar,    . 

Pseudostratified, 
Stratified  Epithelium,    . 

Stratified  Squamous, 

Transitional, 

Stratified  Columnar, 
Modified  Forms  of  Epithelium, 

Ciliated  Epithelium, 

Pigmented  Epithelium,   . 

Glandular  Epithelium,    . 

Neuro-epithelium,    . 
Mesothelium  and  Endothelium. 
Technic,  .... 


and  Endothelium), 


53 
53 
53 
54 
54 
54 
54 
56 
56 
56 
57 
5S 
59 
59 
60 
60 
60 
60 
61 


CHAPTER    III. 

The  Connective  Tissues, ...  63 

Histogenesis, 63 

General  Characteristics, 63 

Classification, 63 

Fibrillar  Connective  Tissue, 64 

Areolar  Connective  Tissue, 67 

Formed  Connective  Tissue, 67 

Development,            ...........  68 

Elastic  Tissue 6S 

Technic  for  Fibrillar  and  Elastic  Tissue,       ......  70 

Embryonal  and  Mucous  Tissue,    .         .         .         .         .         .         .         •         •  71 

Technic, 73 

Recticular  Tissue, 73 


Till 


COA'TENTS. 


Lymphatic  Tissue. 

Technic  for  Reticul 
Fat  Tissue, 

Technic.  . 
Cartilage. 

Hyaline,   . 

Elastic,     . 

Fibrous.   . 

Technic,  . 
Bone  Tissue. 

Technic,  . 
Neuroglia. 


ir  and  Lymphatic  Tissue, 


PAGE 

75 
75 
75 
79 
79 
8o 
Si 
8i 
82 
82 
83 
84 


CHAPTER    IV. 

The  Blood, 85 

Red  Blood  Cells, ' 85 

White  Blood  Cells, 86 

Blood  Platelets, 88 

Development,          ............  S8 

Technic, 89 


CHAPTER   V. 


Muscle  Tissue. 

Involuntary  Smooth  Muscle, 
Voluntary  Striated  Muscle,    . 
Involuntary  Striated  Muscle, 
Development  of  Muscle  Tissue, 
Technic,  .... 


9' 
91 
92 
96 
98 
99 


CHAPTER    VI. 


Nerve  Tissue,    .... 

IOI 

The  Neurone,    .... 

IOI 

General  Structure, 

IOI 

The  Cell  Body, 

. 

IOI 

The  Nucleus,  . 

102 

The  Cytoplasm, 

[03 

Neurofibrils, 

l°3 

Perifibrillar  Substance, 

103 

Chromophilic  Bodies, 

104 

The  Dendrites, 

106 

The  Axone,     .... 

106 

Non-Medullated  Axone  (Non 

Medullated  Nerve  Fibres), 

107 

Medullated  Axones  (Medullated  Nerve  Fibres), 

10S 

Theories  as  to  Physiology  of  the  Neurone, 

1 10 

Neuroglia, 

1 1 1 

'1  e<  Imic.          .......... 

1 12 

General  References, 

"3 

CONTENTS. 


IX 


PART   IV.— THE   ORGANS. 


CHAPTER    I. 

The  Circulatory  System. 
The  Blood-vessel  System, 

General  Structure, 

Capillaries, 

Arteries,  . 

Veins, 

Te clinic,    . 

The  Heart. 
Technic,    . 

Development  of  the  Blood-vessel  System, 
The  Lymph-vessel  System, 

Lymph  Capillaries, 

Lymph  Spaces. 

Serous  Membranes. 

Technic,   . 
The  Carotid  Gland, 
The  Coccygeal  Gland.    . 

Technic.  . 
General  References  on  Circulatory  System, 


PAGE 

17 
17 
17 
17 
:iS 

[24 

J5 

27 

128 

[28 

[29 
-9 

:-'• 


CHAPTER    II. 


Lymphatic  Organs.  . 
The  Lymph  Nodes. 

Technic.  . 
Hannolymph  Nodes, 

Technic.  . 
The  Thymus, 

Technic.  . 
The  Tonsils.   . 

The  Palatine  Tonsils, 

The  Lingual  Tonsils, 

The  Pharyngeal  Tonsils 

Technic,  . 
The  Spleen,    . 

Technic.   . 
General  References. 


131 
131 

134 


jj 


137 
13S 
139 
140 
140 
141 
'4- 
14- 
14- 
146 

147 


CHAPTER  III. 


The  Skeletal  System. 
The  Bones, 
Bone  Marrow, 

Red  Marrow,  . 

Yellow  M arrow . 


14S 
1 48 
152 

>5- 

154 


x  CONTENTS. 

PAGE 

Technic. i$P 

Development  of  Bone 159 

Intracartilaginous  Development, 157 

Intramembranous  Development, 159 

Subperiosteal, i(|- 

Growth  of  Bone, 163 

Technic, 164 

The  Cartilages, 164 

Articulations, 165 

Technic -.         .         .    166 

General  References, 166 

CHAPTER    IV. 
The  Muscular  System. 

A  Voluntary  Muscle, 167 

Tendons, 168 

Tendon  Sheaths  and  Bursa?, 168 

Growth  of  Muscle, 169 

Technic, 169 


CHAPTER    V. 


Glands  and  the  General  Structure  of  Mucous  Membranes,  .        .170 

Glands — General  Structure  and  Classification, 17° 

General  Structure  of  Mucous  Membranes, 174 


CHAPTER   VI. 


The  Digestive  System 

175 

Anatomical  Divisions, 

i/5 

The  Headgut, 

176 

The  Mouth 

176 

The  Mucous  Membrane  of  the  Mouth, 

176 

Glands  of  the  Oral  Mucosa, 

'77 

Technic,             ..... 

'70 

The  Tongue,     ..... 

'79 

Technic,     ..... 

[82 

The  Teeth 

&3 

Development  of  the  Teeth, 

[87 

Technic,     ..... 

,89 

The  Pharynx, 

190 

Technic 

190 

'J  he  Foregut, 

191 

The  (Esophagus, 

i'H 

Technic 

192 

General  Structure  of  the  Walls  of  the  Gastn 

>-intestina 

1  Canal, 

192 

The  Stomach, 

194 

Technic.    ...... 

•    199 

CONTENTS.  xi 

PAGE 

The  Midgut, 20c 

The  Small  Intestine, 20c 

The  Endgut, 206 

The  Large  Intestine, 206 

The  Rectum, 210 

Blood-vessels  of  the  Stomach  and  Intestines, 211 

Lymphatics  of  the  Stomach  and  Intestine,    .         .         .        .         .         -213 

Secretion  and  the  Absorption  of  Fat, 214 

Technic,  .         .         .         .  .         .         .        .        .        .         .         .216 

The  Larger  Glands  of  the  Digestive  System, 217 

The  Salivary  Glands, 217 

The  Parotid 218 

The  Sublingual,        .         .         .        .        .        .         .        .         .         .219 

The  Submaxillary,    .         .         .         .         .         .         .         .         .         .219 

Technic,    .         .         .         .         .         .         .         .         .         .         .         .221 

The  Pancreas,  .         .         .         .         .         .         .         .         .         .         .221 

Technic, 227 

The  Liver, 227 

Excretory  Ducts  of  the  Liver,  .......  233 

The  Gall-bladder, 233 

Development  of  the  Digestive  System, 234 

Technic,  .............  235 

General  References. 236 


CHAPTER   VII. 

The  Respiratory  System 237 

The  Nares, 237 

The  Larynx,  ............  239 

The  Trachea,  ............  239 

Technic,  . 242 

The  Bronchi,  ............  242 

The  Lungs, 244 

Development  of  the  Respiratory  System, 250 

Technic,  .         .         .         .         .         .        .        .         .        .         .        .  251 

The  Thyroid, 251 

The  Parathyroids, 252 

Technic, 253 

General  References,       ...........  253 


CHAPTER    VIII. 

The  Urinary  System, 254 

The  Kidney, 254 

The  Kidney-Pelvis  and  Ureter, 264 

The  Urinary  Bladder, 265 

The  Adrenal, 268 

Technic. 269 

General  References, 269 


Xll 


CONTENTS. 


d  Ejaculatory 
Connected    vvi 


Spermatozoon 


Ducts, 
th    the 


D 


CHAPTER    IX. 

The  Reproductive  System. 
Male  Organs. 
The  Testis, 
The  Seminal  Ducts, 
The  Epididymis. 
The  Yas  Deferens. 
The  Seminal  Vesicles  an 
Rudimentary   Structures 

Genital  System, 
The  Spermatozoon, 

Development  of  the 
Technic,   . 
The  Prostate  Gland, 
Cowper's  Glands,     . 

Technic,     . 
The  Penis, 
The  Urethra,    . 
Technic,  . 
Female  Organs, 
The  Ovary, 
Rudimentary    Structures 

Genital  System, 
The  Oviduct,    . 
Technic,     . 
The  Uterus, 

The  Mucosa  of  the  Resting  Uterus, 
The  Mucosa  of  the  Menstruating  Uterus 
The  Mucosa  of  the  Pregnant  Uterus, 
The  Placenta,     .... 

The  Vagina,     ...... 

Development  of  the  Urinary  and  Reproductive  Systems 

Technic, 

( ieneral  References, 


Connected    w 


evelopment  o 


ith   the    Development  o 


TAGE 

270 
270 
270 
276 
276 
277 


the 


f   the 


CHAPTER   X. 


Tin-:  Skix  and  its  Appendages, 
The  Skin,         .... 

Technic,   .... 
I  he  Nails,       .... 

Technic, 
The  Hair,        .... 

I  >■<  In) ic,   .... 
Development  of  Skin,  Nails,  and 
1  In    Mammary  Gland,    . 

Technic,  .... 
( reneral  References, 


1  lair, 


CONTENTS. 


xm 


CHAPTER   XI. 


the 


Posterior 


Col 


al  Nervous  System 


The  Nervous  System, 

Histological  Development,    . 
Membranes  of  the  Brain  and  Cord, 
Technic,  .... 

The  Ganglia,  .... 

Technic,  .... 

The  Peripheral  Nerves, 

Technic, 

The  Spinal  Cord,    .... 

Technic, 

General  Structure  and  Practical  Study, 
Origin  of  the  Fibre  Tracts  of  the  Cord, 

The  Spinal  Ganglion  Cell  and  the  Origin  of 
umns,   .... 
Afferent  Nerve  Terminations, 
Cells   Situated  in  Other  Parts  of  the  Centr 

which  Contribute  Axones  to  the  White  Matter  of  the  Cord, 
Root  Cells — Motor  Cells  of  the  Anterior  Horn, 
Column  Cells,    . 
Cells  of  Golgi,  Type  II., 
Technic  and  Practical  Study, 
Fibre  Tracts  of  the  Cord, 
Ascending  Fibre  Tracts, 
Descending  Fibre  Tracts, 
Fundamental  Columns,     . 
Technic,     .... 
The  Medulla  Oblongata  (including  the 
General  Structure,   . 
Technic,   ..... 
Practical  Study, 

Transverse  Section  through  Pyramidal  Decussation, 
Transverse  Section  through  Sensory  Decussation, 
Transverse  Section  through  Lower  Part  of  Olivary  Nucleus 
Transverse  Section  through  Middle  of  Olivary  Nucleus. 
Transverse  Section  through  Exit  of  Cranial  Nerve  VIII., 
Transverse  Section  through  Exits  of  Cranial  Nerves  VI.  and 
Transverse  Section  through  Exit  of  Cranial  Nerve  V., 

The  Midbrain, 

General  Structure, 

Practical  Study 

Transverse  Section  through  Exit  of  Cranial  Nerve  IV., 
Transverse  Section  through  Exit  of  Cranial  Nerve  III., 
The  Cerebral  Peduncles,        .... 

The  Cerebellum 

General  Histology  of  the  Cerebellar  Cortex, 
The  Cerebrum,        ...... 

General  Histology  of  the  Cerebral  Cortex, 
Technic,  ...... 


Pons  Varolii), 


VII 


332 
333 
334 
335 
335 
338 
338 
340 
340 
340 
34i 
346 

346 
348 

352 
352 
353 
356 
356 
358 
360 
362 

364 
366 

367 
367 
369 
37° 
37°' 
37i 
376 
378 
381 
3S4 
388 

39i 
39i 
391 
391 

394 
396 
397 
397 
402 
402 
407 


XIV 


CON  TENTS. 


PAGE 

The  Pituitary  Body 410 

The  Pineal  Body. 411 

Technic,  .         .         .        .         .         .         .         .         .        .         .         .         .411 

General  References, 411 


CHAPTER  XII. 


Tin:  Organs  of  Special  Sense, 
The  Organ  of  Vision,     . 

The  Eyeball,    . 

The  Optic  Nerve,     . 

The  Relations  of  Optic  Nerv 

The  Lacrymal  Apparatus, 

The  Eyelid. 

Development  of  the  Eye, 

Technic,  . 
The  Organ  of  Hearing, 

The  External  Ear, 

The  Middle  Ear, 

The  Internal  Ear, 

Development  of  the  Ear 

Technic, 
The  Organ  of  Smell. 

Technic,   . 
The  Organ  of  Taste, 

Technic,  . 
General  References, 

Index, 


to  Retina  and 


Bra 


412 
412 
412 
424 
424 
429 
43° 
43  > 
43- 
433 
433 
434 
435 
444 
445 
446 

448 

44S 
449 
449 

45i 


PART  I. 
HISTOLOGICAL  TECHNIC. 


CHAPTER  I. 
GENERAL   TECHNIC. 

Certain  body  fluids,  blood,  urine,  etc.,  may  be  examined  by 
simply  placing  them  on  a  slide  under  a  cover-glass.  A  few  tissues, 
such  as  thin  membranes,  e.g.,  omentum  and  mesentery,  may  be  ex- 
amined fresh  in  some  inert  fluid,  as  normal  salt  solution  (0.75  per 
cent  aqueous  solution  sodium  chorid).  Most  tissues  and  organs, 
however,  require  more  or  less  elaborate  preparation  to  render  them 
suitable  for  microscopic  examination.  Tissues  too  dense  and  thick 
to  be  readily  seen  through  with  the  microscope  must  be  rendered 
more  transparent.  This  is  accomplished  by  pulling  the  tissue  apart 
into  fine  shreds,  teasing,  or  by  cutting  it  into  thin  slices,  section  ait- 
ting.  Some  tissues  admit  of  teasing  in  a  fresh  condition  ;  others  can 
be  satisfactorily  teased  only  after  they  have  been  subjected  to  the 
action  of  a  chemical  which  breaks  down  the  substance  holding  the 
tissue  elements  together,  maceration.  Fresh  tissue  can  rarely  be  cut 
into  sections  sufficiently  thin  for  microscopic  examination.  It  must 
be  first  killed  in  such  a  manner  as  to  preserve  as  nearly  as  possible 
the  living  tissue  relations,  fixation.  If  too  soft  it  must  be  hardened, 
or  if,  as  is  the  case  with  bone,  it  is  too  hard,  it  must  be  softened  by 
dissolving  out  the  mineral  salts,  decalcification.  If  very  thin  sec- 
tions are  to  be  cut,  it  is  further  necessary  to  impregnate  the  tissue 
with  some  fluid  substance  which  will  harden  in  the  tissue  and  give 
to  the  mass  a  firm,  even  consistence.     This  is  known  as  embedding. 

Again,  most  tissue  elements  have  refractive  indices  which  are  so 
similar,  that  their  differentiation  is  often  extremely  difficult.  To 
overcome  this  difficulty  recourse  is  had  to  staining  the  tissue  with 
dyes  which  have  an  affinity  for  certain  only  of  the  tissue  elements, 
or  which  stain  different  elements  with  different  degrees  rf  intensity. 
This  is  known  as  differential  or  selective  staining. 

Only  the  more  common   procedures  used   in  the  preparation  of 

3 


4  HISTOLOGICAL    TECH  NIC. 

tissues  for  microscopic  study  are  described  in  this  section.  For 
other  methods  the  student  is  referred  to  special  works  upon  micro- 
scopic technic. 

I.  Dissociation  of  Tissue  Elements. 

This  is  accomplished  by  (i)  teasing,  (2)  maceration. 

(1)  Teasing. — This  consists  in  pulling  apart  fresh  or  preserved 
tissues  by  means  of  teasing  needles.  Instructive  specimens  of  such 
tissues  as  muscle  and  nerve  may  be  obtained  in  this  way. 

(2)  Maceration. — This  is  the  subjecting  of  a  tissue  to  the  action 
of  some  chemical  which  breaks  down  the  substance  uniting  the  tis- 
sue elements,  thus  allowing  them  either  to  fall  apart  or  to  be  more 
easily  dissociated  by  teasing.  The  most  commonly  used  macerating 
fluids  are  : 

(a)  Ranvicrs  Alcohol  (33  per  cent,  made  by  adding  35  c.c. 
of  96-per-cent  alcohol  to  65  c.c.  of  water).. — Bits  of  fresh  tissue 
are  placed  in  this  fluid  for  from  twenty-four  to  forty-eight  hours. 
The  cells  may  then  be  easily  separated  by  shaking  or  to  by  teasing. 
Ranvier's  alcohol  is  an  especially  satisfactory  macerating  fluid  for 
epithelia. 

(b)  Formalin,  in  very  dilute  solutions  (0.2  to  0.4  per  cent). — 
Tissues  should  remain  in  the  formalin  solution  from  twenty-four  to 
forty-eight  hours.  This  also  is  especially  useful  for  dissociating 
epithelial  cells. 

(c)  Sodium  or  Potassium  Hydrate  (30  to  35-per-cent  aqueous 
solution). — From  twenty  minutes  to  an  hour  is  usually  sufficient 
to  cause  the  tissue  elements  to  fall  apart  or  to  be  readily  pulled 
apart  with  the  teasing  needles.  If  it  is  at  any  time  desirable 
to  stop  the  action  of  the  caustic  alkali,  this  may  be  accomplished  by 
neutralizing  with  glacial  acetic  acid  or  by  replacing  the  alkali  with 
a  60-per-cent  aqueous  solution  of  potassium  acetate.  The  speci- 
mens may  then  be  preserved  in  the  potassium  acetate  solution,  in 
glycerin,  or  in  50-per-cent  alcohol.  This  dissociating  fluid  is  largely 
used  for  muscle  cells  and  fibres. 

II.  Fixation. 

Fixation  consists  in  so  treating  a  tissue  as  to  preserve  as  nearly 
as  possible  its  living  structure.  This  is  usually  accomplished  by 
means  of  chemicals  in  solution,  the  solution  being  known  as  a  fixa- 


GENERAL    TECHNIC.  5 

tive.  In  fixation  small  pieces  of  tissue  should  be  placed  in  large 
quantities  of  the  fixative.  Organs  or  even  bodies  may  be  fixed  in 
toto  by  injecting  the  fixative  through  an  artery  and  allowing  it  to 
escape  through  a  vein.  After  fixation  by  injection  the  specimen 
should  be  placed  in  a  large  quantity  of  the  same  fixative.  The  time 
required  for  fixation  depends  upon  the  character  of  the  tissue  and 
upon  the  fixative  used. 

The  following  are  the  fixatives  in  most  common  use  : 
(i)  Strong  Alcohol  (96  per  cent). — This  is  used  to  fix  small 
pieces  of  tissue.  It  is  a  rapid  fixative  requiring  from  two  to  twenty- 
four  hours.  The  tissue  is  at  the  same  time  hardened  so  that  at  the 
end  of  this  time  it  is  ready  for  embedding.  As  good  fixation  is  de- 
pendent upon  keeping  the  alcohol  up  to  its  full  strength,  it  is  best  to 
change  the  alcohol  after  from  two  to  four  hours. 

(2)  Dilute  Alcohol  (30  to  80  per  cent). — This  is  probably  the 
most  used  of  all  fixatives.  It  does  not  give  satisfactory  results, 
causing,  as  a  rule,  much  shrinkage. 

(3)  Formalin  (2-per-cent  to  10-per-cent  aqueous  solutions). — Fix- 
ation is  accomplished  in  from  six  to  twenty-four  hours.  Formalin 
is  a  quick  fixative  of  good  penetrating  powers.  It  acts  better  when 
used  in  mixtures  with  other  fixatives  than  when  used  alone. 

(4)  Muller's  Fluid. 

Potassium  bichromate 2.5  gm. 

Sodium  sulphate 1.0  gm. 

Water 100.0  c.c. 

Tissues  remain  in  this  fluid  from  a  week  to  several  months.  Large 
quantities  of  the  fixatives  should  be  used  and  frequently  renewed. 

Muller's  fluid  finds  one  of  its  most  important  uses  in  fixing 
nerve  tissue.  Good  fixation  of  fairly  large  pieces  of  tissue  may  be 
obtained. 

(5)  Formalin- Mailer  s Fluid  {Ortlis  Fluid). — In  this  fluid  a  2.5- 
per-cent  aqueous  solution  of  formalin  replaces  the  water  of  the  pre- 
ceding formula.  It  should  be  freshly  prepared,  or,  if  more  conven- 
ient, a  double-strength  Muller's  fluid  and  a  5-per-cent  formalin  solu- 
tion maybe  kept  in  stock.  Orth's  fluid  can  then  be  made  by  taking 
equal  parts  of  each.  The  action  of  this  fixative  is  similar  to  that  of 
Muller's  fluid.  It  has  the  advantage  of  fixing  more  quickly  and  of 
possessing  greater  penetrating  power.  It  is  one  of  the  best  general 
fixatives,  and  is  also  largely  used  for  fixing  nerve  tissue. 


6  HISTOLOGICAL    TECH  NIC. 

(6)  Osmic  Acid. — This,  in  a  i-per-cent  aqueous  solution,  is  a 
quick  fixative  of  poor  penetrating  power.  Very  small  pieces  of  tis- 
sue must  therefore  be  used.  They  should  remain  in  the  fluid  from 
twelve  to  twenty-four  hours.  Osmic  acid  stains  fat  and  myelin  black 
and  is  consequently  useful  in  demonstrating  their  presence  in  tissues. 
Fixation  should  take  place  in  the  dark. 

(;)  Flemmings  Fluid. 

Chromic  acid,  i-per-cent  aqueous  solution.    25  c.c. 

Osmic  acid,  i-per-cent  aqueous  solution 10  c.c. 

Glacial  acetic  acid,  i-per-cent  aqueous  solution 10  c.c. 

Water 55  c.c. 

As  this  is  an  osmic-acid  mixture,  small  pieces  of  tissue  should  be 
used  and  the  solution  should  be  freshly  made. 

Flemming's  fluid  is  one  of  the  best  fixatives  for  nuclear  struc- 
tures, and  is  of  especial  value  in  demonstrating  mitotic  figures.  Tis- 
sues should  remain  in  the  fluid  for  about  three  days. 

(8)  Mercuric  Chlorid. — This  may  be  used  either  in  saturated 
aqueous  solution  or  in  saturated  solution  in  0.75-per-cent  salt  solution. 
Fixation  is  complete  in  from  twelve  to  twenty-four  hours. 

A  saturated  solution  of  mercuric  chlorid  in  5-per-cent  aqueous 
solution  of  glacial  acetic  acid  also  gives  excellent  results. 

(9)  Zenker  s  Fluid. 


Potassium  bichromate 2.5  gm. 

Sodium  sulphate 1.0  gm. 

Mercuric  chlorid 5.0  gm. 

Hydric  acetate   5.0  c.c. 

Water 100.0  c.c. 

This  fluid  should  be  freshly  made,  or  the  salts  may  be  kept  in  solu- 
tion and  the  hydric  acetate  added  at  time  of  using. 

Fixation  requires  from  two  to  twenty-four  hours. 

(10)  Picric  acid  \&  an  excellent  fixative  for  cytoplasm.  It  may 
be  used  in  :  (a)  Saturated  aqueous  solution,  requiring  subsequent 
hardening  in  alcohol  without  washing  in  water;  (/;)  saturated  solu- 
tion of  picric  acid  in  i-per-cent  aqueous  solution  of  acetic  acid;  (c) 
saturated  solution  of  picric  acid  in  2-per-cent  aqueous  solution  of 
sulphuric  acid. 


GENERAL    TECHNIC.  7 

III.  Hardening. 

Most  fixatives  are  also  hardening  agents  if  their  action  be  pro- 
longed. This  is,  however,  often  detrimental.  For  this  reason  it  is 
customary,  after  fixation  is  complete,  to  transfer  the  specimens,  with 
or  without  washing,  to  a  second  fluid  for  the  purpose  of  hardening. 

The  most  commonly  used  hardening  agent  is  alcohol. 

When  strong  alcohol  is  used  as  a  fixative  no  washing  is  neces- 
sary.    The  alcohol  should,  however,  be  changed. 

After  fixation  in  dilute  alcohol,  hardening  should  be  accomplished 
by  carrying  the  tissue  through  successively  stronger  alcohols  ending 
with  96  per  cent.  This  is  known  as  hardening  by  means  of  "graded 
alcohols."  The  first  alcohol  should  be  40  per  cent  to  50  per  cent, 
the  second  70  per  cent,  the  third  80  per  cent,  the  last  96  per  cent. 
With  very  delicate  tissues  the  gradations  may  be  less  rapid.  In 
each  of  the  alcohols  the  specimens  should  remain  for  from  twelve  to 
twenty-four  hours. 

After  fixation  with  formalin,  specimens  may  be  either  carried 
through  graded  alcohols  or  transferred  at  once  to  strong  alcohol.  At 
least  forty-eight  hours  is  required  for  hardening  formalin-fixed  tis- 
sues. Specimens  fixed  in  osmic  acid  should  be  washed  from  one  to 
two  hours  in  running  water,  then  carried  through  graded  alcohols. 

Tissues  fixed  in  any  of  the  solutions  containing  chromic  acid  or 
potassium  bichromate  should  be  thoroughly  washed  in  running  water 
and  hardened  in  graded  alcohols.  This  hardening  is  best  done  in 
the  dark. 

After  mercuric  chlorid  and  Zenker's  fluid  fixations  the  tissue  is 
thoroughly  washed  and  passed  through  graded  alcohols.  Wrhen  80- 
per-cent  alcohol  is  reached,  a  small  quantity  of  iodin  is  added  to 
the  alcohol  to  remove  all  trace  of  the  mercury.  As  the  alcohol  be- 
comes clear,  more  iodin  is  added  until  the  alcohol  remains  slightly 
tinged.      The  specimen  is  then  transferred  to  strong  alcohol. 

IV.  Preserving. 

Hardened  tissues  are  usually  preserved  in  80-per-cent  alcohol. 
Formalin  in  aqueous  solutions  of  1  per  cent  to  10  per  cent  is  also 
used  as  a  preservative. 


HISTOLOGICAL    TECH  NIC. 


V.  Decalcifying. 

Tissues,  such  as  bone  and  teeth  which  contain  lime  salts,  require 
further  treatment  before  sections  can  be  cut.  The  object  is  to  dis- 
solve out  the  lime  salts.      This  is  known  as  decalcification. 

Tissues  to  be  decalcified  must  be  first  fixed  and  hardened.  For 
bone,  fixation  in  formalin-Muller's  fluid  and  hardening  in  graded  al- 
cohols give  good  results.  After  hardening,  the  tissue  is  washed  in 
water  and  placed  in  one  of  the  following  decalcifying  fluids.  The 
quantity  of  fluid  should  always  be  large  and  the  fluid  frequently 
changed.  The  completion  of  decalcification  can  be  determined  by 
passing  a  needle  through  the  specimen  or  by  cutting  it  with  a  scal- 
pel. The  time  required  varies  with  the  size  and  hardness  of  the 
specimen  and  the  decalcifying  fluid  used. 

(i)  Hydrochloric  Acid. — This  may  be  used  in  aqueous  solutions 
of  from  0.5  per  cent  to  5  per  cent.  A  very  satisfactory  decalcifying 
mixture  is  that  known  as  Ebner's  hydrochloric-salt  solution.  It 
consists  of  : 

Sodium  chlorid,  saturated  aqueous  solution. 1  part. 

Water 2  parts. 

Hydrochloric  acid,  sufficient  to  make  a  from  2-per-cent  to  5-per- 
cent solution. 

The  addition  of  the  salt  prevents  swelling  of  the  tissue.  This 
fluid  is  slow  in  acting  and  should  be  frequently  changed.  When 
decalcification  is  complete,  the  specimen  is  washed  in  sufficient 
changes  of  water  to  remove  all  trace  of  acid.  This  may  be  quickly 
accomplished  by  the  addition  of  a  little  ammonium  hydrate  to  the 
water.      The  specimen  is  then  carried  through  graded  alcohols. 

(2)  Nitric  Acid. — This  is  less  used  than  the  preceding.  The 
strength  should  be  from  1  per  cent  to  10  per  cent  aqueous  solution. 
Weak  solutions  ( 1  per  cent  to  2  per  cent)  will  decalcify  small  fcetal 
bones  in  from  three  to  twelve  days.  For  larger  bones  stronger  solu- 
tions and  longer  time  are  required. 

(3)  Small  bones  maybe  satisfactorily  decalcified  in  Zenker  s  fluid 
(see  fixatives,  page  6),  or  in  the  following : 

Picric  acid 1  part. 

Chromic  acid J  part. 

Clacial  acetic  acid 5  parts. 


GENERAL    TECHNIC. 


VI.  Embedding. 

Most  hardened  tissues  are  still  too  soft  to  be  easily  cut  into  the 
thin  sections  desirable  for  microscopic  study.  In  order  to  support 
the  tissue  elements  and  render  them  more  firm  for  section  cutting, 
recourse  is  had  to  "  embedding."  This  consists  in  impregnating  the 
tissues  with  some  substance  which  is  liquid  when  the  tissues  are 
placed  in  it,  but  which  can  be  made  to  solidify  throughout  the  tis- 
sues. In  this  way  the  tissue  elements  are  held  firmly  in  place. 
The  embedding  substances  most  used  are  celloidin  and  paraffin. 

Celloidin  Embedding. 

(i)  Alcohol-Ether  Celloidin. — Three  solutions  should  be 
made. 

Solution  No.  J.  Thick  celloidin- — a  5 -per- cent  solution  of  cel- 
loidin in  equal  parts  alcohol  and  ether. 

Solution  No.  2.  Medium  celloidin — made  by  diluting  solution 
No.  3  with  an  equal  volume  of  equal  parts  alcohol  and  ether. 

Solution  No.  I.  Thin  celloidin — made  by  diluting  solution  No.  2 
with  an  equal  volume  of  equal  parts  of  alcohol  and  ether. 

The  hardened  tissues  are  placed  successively  in : 

Strong  alcohol,  twelve  to  twenty-four  hours. 

Equal  parts  alcohol  and  ether,  twelve  to  twenty-four  hours. 

Thin  celloidin,  twenty-four  hours  or  longer. 

Medium  celloidin,  twenty-four  hours  or  longer. 

Thick  celloidin,  twenty-four  hours  or  longer. 

The  exact  time  tissues  should  remain  in  the  different  grades  of 
celloidin  depends  upon  the  character  of  the  tissue,  the  size  of  the 
specimen,  and  the  thinness  of  section  desired.  Many  tissues  may 
be  advantageously  left  for  days,  or  even  weeks,  in  thin  or  medium 
celloidin. 

The  celloidin  must  now  be  Jiardened  and  the  specimen  blocked. 
By  the  latter  is  meant  fastening  the  embedded  specimen  to  a  block 
of  wood  or  other  suitable  material  which  may  be  clamped  in  the 
microtome  (see  section  cutting).  The  specimen  may  be  taken  from 
the  thick  celloidin,  considerable  of  the  latter  adhering  to  the  speci- 
men, quickly  pressed  upon  a  block  of  wood  or  vulcanized  fibre,  al- 


io  HISTOLOGICAL    TECIINIC. 

lowed  to  harden  five  to  ten  minutes  in  air  and  then  immersed  in 
8o-per-cent  alcohol.  The  alcohol  gives  an  even  hardening  of  the 
celloidin,  attaching  the  specimen  firmly  to  the  block.  Another 
method,  and  one  by  which  very  even-shaped  blocks  may  be  obtained, 
is  to  place  the  specimen  from  the  thick  celloidin  into  a  little  paper 
box  (made  by  folding  paper  over  a  wooden  block),  slightly  larger  than 
the  specimen,  and  covering  with  thick  celloidin.  The  celloidin 
should  dry  slowly  under  a  bell- jar  for  from  two  to  twelve  hours,  ac- 
cording to  the  amount  of  celloidin,  after  which  it  should  be  im- 
mersed in  8o-per-cent  alcohol  and  the  paper  pulled  off.  Such  a 
block  may  be  cut  into  any  desired  shape.  It  is  attached  to  the 
wooden  or  vulcanized  block  by  clipping  for  a  moment  in  thick  cel- 
loidin, and  then  pressing  firmly  clown  upon  the  block.  After 
five  to  ten  minutes'  drying  in  air  it  is  transferred  to  8o-per-cent 
alcohol. 

Old,  hard,  celloidin-embedded  specimens  are  sometimes  difficult 
to  attach  to  blocks.  This  may  usually  be  accomplished  by  first  thor- 
oughly drying  the  specimen  and  then  dipping  it  in  equal  parts  alco- 
hol and  ether.  This  softens  the  celloidin,  after  which  the  specimen 
is  dipped  in  thick  celloidin  and  blocked. 

(2)  Clove-oil  Celloidin. — A  more  rapid  impregnation  of  the 
tissue  may  be  obtained  by  means  of  what  is  known  as  clove-oil 
celloidin. 

Celloidin 30  gin. 

Clove  oil. 100  gin. 

Ether 400  gm. 

Alcohol,  absolute 20  gm. 

The  celloidin  is  first  placed  in  a  jar  and  the  clove  oil  and  ether 
added.  From  two  to  four  days  are  required  for  solution  of  the  cel- 
loidin. During  this  time  the  jar  should  be  shaken  several  times. 
After  the  celloidin  is  dissolved  the  absolute  alcohol  is  added  and  the 
solution  is  ready  for  use. 

The  specimen  must  be  thoroughly  dehydrated  and  transferred 
from  strong  alcohol  to  the  clove-oil  celloidin.  From  six  to  twelve 
hours  is  sufficient  to  impregnate  small  pieces  of  tissue.  The  tissue 
is  now  taken  from  the  celloidin,  placed  directly  upon  a  wooden  or 
vulcanized  block,  and  immersed  in  chloroform.  The  celloidin  har- 
dens in  from  three  to  five  minutes,  and  is  then  ready  for  sectioning. 
Extremely  thin  sections  may  be  cut. 


GENERAL    TECHNIC.  H 

A  disadvantage  in  clove-oil  celloidin  is  that  neither  the  blocks 
nor  the  sections  can  be  kept  permanently  in  alcohol,  as  can  those 
embedded  in  alcohol-ether  celloidin.  They  may,  however,  be  kept 
in  pure  chloroform. 

Paraffin  Embedding. 

Paraffin,  the  melting-point  of  which  is  from  500  to  550  C,  is  used. 
In  very  warm  weather  it  may  be  necessary  to  add  to  this  a  little 
paraffin  whose  melting-point  is  62 °  C.  For  paraffin  embedding  a 
thermostat  or  paraffin  oven  is  necessary  in  order  that  a  constant 
temperature  may  be  maintained. 

The  hardened  tissue  is  first  completely  dehydrated  in  absolute 
alcohol.  It  is  then  transferred  to  some  solvent  of  paraffin.  For 
this  purpose  xylol,  chloroform,  or  a  mixture  of  1  part  chloroform 
to  2  parts  absolute  alcohol  may  be  employed.  Depending  upon 
whether  xylol  or  chloroform  is  used,  the  tissue  is  next  transferred  to 
a  saturated  solution  of  paraffin  in  xylol  or  in  chloroform.  Tissues 
should  remain  in  xylol-paraffin  from  one-half  to  one  hour;  in  chloro- 
form-paraffin from  one  to  three  hours.  The  tissue  is  next  trans- 
ferred to  melted  paraffin,  where  it  remains  from  one  to  three  hours, 
according  to  its  size  and  density.  Tissues  should  be  allowed  to 
remain  in  the  melted  paraffin  only  long  enough  for  complete  impreg- 
nation, and  the  paraffin  should  be  kept  at  the  lowest  temperature 
consistent  with  complete  fluidity. 

Except  for  very  delicate  tissues,  the  xylol-paraffin  and  chloro- 
form-paraffin maybe  omitted,  the  specimen  being  transferred  directly 
from  xylol  or  chloroform  to  melted  paraffin. 

For  hardening  the  paraffin  a  very  convenient  apparatus  consists 
of  a  plate  of  glass  and  several  L-shaped  pieces  of  iron  or  lead.  Two 
of  these  are  placed  on  the  glass  plate  in  such  a  manner  as  to  enclose 
a  space  of  the  desired  size.  Into  this  are  placed  the  specimen  and 
sufficient  melted  paraffin  to  cover  it.  Both  glass  and  irons  should 
be  smeared  with  glycerin  to  prevent  the  paraffin  from  adhering,  and 
should  be  as  cold  as  possible,  so  that  the  paraffin  may  harden  quickly. 
The  same  paper  boxes  described  under  celloidin  embedding  may  also 
be  used  for  paraffin.  Another  good  method  for  small  pieces  of  tissue 
is  to  place  the  specimen  in  paraffin  in  an  ordinary  watch-glass  which 
has  been  coated  with  glycerin.  Both  paper-box  and  watch-glass 
specimens  are  immersed  in  cold  water  as  soon  as  the  surface  of  the 


12  HISTOLOGICAL    TECH'S  I C. 

paraffin  has  become  hard.      After  the  paraffin  has  hardened  any  ex- 
cess may  be  cut  away  with  a  knife. 

Paraffin-embedded  specimens  may  be  kept  indefinitely  in  air. 
For  section  cutting  the  block  of  paraffin  is  attached  to  a  block  of 
wood  or  of  vulcanite  or  to  the  metallic  block-holder  of  the  micro- 
tome. This  is  done  by  heating  one  surface  of  the  paraffin  until  it 
becomes  soft  and  then  pressing  this  side  down  firmly  upon  the  block. 

VII.  Section  Cutting. 

The  older  method  of  making  free-hand  sections  with  a  razor  has 
been  almost  completely  superseded  by  the  use  of  a  cutting  instru- 
ment known  as  the  microtome.  This  consists  essentially  of  a  clamp 
for  holding  the  specimen  and  a  microtome  knife  or  razor.  The  two 
are  so  arranged  that  when  knife  and  specimen  meet  a  section  of  any 
desired  thickness  may  be  cut. 

The  technic  of  section  cutting  differs  according  to  whether  the 
specimen  is  embedded  in  celloidin  or  in  paraffin. 

In  cutting  celloidin  sections  the  knife  is  so  adjusted  that  it  passes 
obliquely  through  the  specimen,  as  much  as  possible  of  the  cutting 
edge  being  used.  The  knife  is  kept  flooded  with  8o-per-cent 
alcohol  and  the  specimens  are  removed  by  means  of  a  camel's-hair 
brush  to  a  dish  of  8o-per-cent  alcohol  where  they  may  be  kept  for 
some  time  if  desired.  When  celloidin  sections  tear  or  when  very 
thin  sections  are  desired,  it  is  often  of  advantage  to  paint  the  surface 
of  the  block  after  cutting  each  section  with  a  coat  of  very  thin 
celloidin. 

Celloidin  sections  are  usually  not  thinner  than  10  //.,  although 
under  favorable  conditions  sections  5  ft  1  or  even  3  <i.  in  thickness  may 
be  obtained. 

In  cutting  paraffin  sections  the  knife  is  kept  dry  and  is  passed 
not  obliquely  but  straight  through  the  specimen,  only  a  small  part  of 
the  cutting  edge  being  used.  An  exception  is  made  in  the  case  of 
very  large  paraffin  sections,  where  an  oblique  knife  is  used.  Sec- 
tions are  removed  from  the  knife  by  a  dry  or  slightly  moistened 
brush.  If  not  desired  for  immediate  use  the  sections  may  be  con- 
veniently kept  for  a  short  time  on  a  piece  of  smooth  paper.  If  sec- 
tions  curl   they  may  be   flattened   by  floating  on  warm   30-per-cent 

1  //  =  micron  =  -j^  of  a  millimetre  =  microscopic  unit  of  measure. 


GENERAL    TECHNIC.  13 

alcohol  or  on  warm  water.  Such  sections  are  then  placed  on  a  slide 
and  dried  in  a  thermostat  at  a  temperature  below  the  melting-point 
of  the  paraffin.  Curling  of  specimens  may  also  be  prevented  by 
holding  the  first  cut  edge  of  the  section  against  the  knife  with  a 
camel's-hair  brush. 

Paraffin  sections  may  be  so  cut  that  the  edges  of  the  sections 
adhere.  Long  series  or  "ribbons"  of  sections  may  thus  be  secured. 
This  is  of  decided  advantage  when  serial  sections  are  desired.  In 
some  cases  when  sections  cut  poorly  or  fail  to  adhere  in  ribbons,  re- 
course may  be  had  to  coating  the  surface  of  the  block  with  a  paraffin 
of  lower  melting-point  than  that  used  for  the  embedding.  A  similar 
effect  may  be  obtained  by  holding  a  heated  metal  plate  or  bar  near 
the  block  until  the  paraffin  is  slightly  softened.  This  process  may 
be  repeated  as  often  as  necessary.  In  addition  to  the  ability  to  cut 
ribbon  seiies,  paraffin  also  has  the  advantage  over  celloidin  in  that 
thinner  sections  may  be  obtained. 

VIII.  Staining. 

This  is  for  the  purpose  of  more  readily  distinguishing  the  differ- 
ent tissue  elements  from  one  another  by  their  reactions  to  certain 
dyes. 

Based  upon  their  action  upon  the  different  tissue  elements,  stains 
may  be  classified  as  (1)  nuclear  dyes,  which  stain  nuclear  structures; 
and  (2)  plasma  dyes,  which  stain  the  cell  body  or  cytoplasm.  Plasma 
dyes  also,  as  a  rule,  stain  the  intercellular  tissue  elements,  and  are 
therefore  known  as  diffuse  stains. 

The  dyes  most  frequently  used  for  staining  tissues  are : 

I.  Nuclear  dyes :  (a)  Hematoxylin  and  its  active  principle, 
haematin ;  (b)  carmine  and  its  active  principle,  carminic  acid; 
(r)  Basic  aniline  dyes. 

II.  Plasma  dyes  :   {a)  Eosin;   (&)  picric  acid;   (c)  acid  aniline  dyes. 
I.  Nuclear  Dyes. — (a)  Hematoxylin. 

1.   Gage  s  Hematoxylin. 

Ammonia  or  potash  alum   ,    7.5  gm. 

Distilled  water 200.0  c.c. 

Boil  for  ten  minutes  to  sterilize ;  cool  and  add  the  following  solution : 

Hematoxylin  crystals   o.  1  gm. 

Alcohol  95  per  cent 10. o  c.c. 

Four  grams  chloral  hydrate  are  then  added  to  the  mixture  to  prevent  growth  of 
fferms. 


14  HISTOLOGICAL    TECH  NIC. 

This  dye  may  be  used  in  full  strength  or  diluted  with  alum  water. 
It  stains  in  from  two  to  five  minutes. 

2.  Delaficld  s  Hematoxylin. 

Hematoxylin  crystals     i  gm. 

Alcohol  6  c.c. 

Ammonia  alum,  saturated  aqueous  solution ioo  c.c. 

The  hematoxylin  should  be  first  dissolved  in  the  alcohol  and 
then  added  to  the  alum  solution.  The  mixture  should  next  be  al- 
lowed to  stand  in  the  light  for  from  seven  to  ten  days  to  ripen.  It 
is  then  filtered,  and  to  the  filtrate  are  added : 

Glycerin 25  c.c. 

Wood  naphtha 25  c.c. 

The  mixture  is  again  allowed  to  stand  for  from  two  to  four  days 
and  filtered.  It  may  be  used  full  strength  or  diluted  with  equal 
parts  of  water.      It  stains  in  from  two  to  five  minutes. 

3 .  Heidenhain '  s  Hematoxylin. 

Hematoxylin  crystals . .        1  gm. 

Water 100  c.c. 

Sections  are  first  placed  for  from  four  to  eight  hours  in  a  2.  5-per- 
cent aqueous  solution  of  ammonium  sulphate  of  iron.  They  are  then 
washed  in  water  and  transferred  to  the  hematoxylin  solution  for  from 
twelve  to  twenty-four  hours.  The  sections  which  are  now  perfectly 
black  are  washed  in  water  and  differentiated  by  again  placing  in  the 
iron  solution  till  they  have  a  light  grayish  color.  After  this  they 
are  thoroughly  washed  in  water. 

4.  Mayer  s  Hcemalnm. 

Haematin ....  1  gm. 

Alcohol.  50  c.c. 

.Ammonium  alum.  5-per-ccnt  aqueous  solution 1.000  c.c. 

The  haematin  is  first  dissolved  in  the  alcohol,  after  which  the  alum 
is  added.  This  dye  does  not  require  any  ripening,  and  is  thus 
available  for  immediate  use.  It  is  a  rapid  nuclear  dye  usually  re- 
quiring not  more  than  from  three  to  five  minutes. 

5.  A  combination  of  Gage's  and  Mayer's  formulas  makes  a  very 
satisfactory  nuclear  dye. 

Haematin 5  gm- 

Alcohol     50  c.c. 

Chloral  hydrate 20  gm. 

Ammonia   alum,   5-per-cent    aqueous  solution   (steril- 
ized)   1. 000  c.c. 


GENERAL    TECHNIC.  15 

The  hasmatin  is  first  dissolved  in  the  alcohol  and  then  added  with 
the  chloral  hydrate  to  the  alum   solution.     This  solution  is  used  in 
full  strength  and  stains  in  from  three  to  five  minutes. 
{b)  Alum-carmine. 

Carmine     2  gm. 

Alum 5  gm. 

Carbolic  acid  .    2  gm. 

Water ...      100  c.c. 

The  alum  is  first  dissolved  in  the  100  c.c.  of  warm  distilled  water. 
This  mixture  is  then  boiled  for  twenty  minutes,  allowed  to  cool,  and 
filtered.  The  carbolic  acid  is  then  added.  This  is  a  slow-acting 
pure  nuclear  dye. 

(c)  Basic  Aniline  Dyes — gentian  violet,  methyl  violet,  methyl 
green,  methyl  blue,  toluidin  blue,  fuchsin,  thionin,  safronin,  etc. 

These  are  best  kept  in  stock  in  saturated  alcoholic  solutions. 
When  desired  for  use,  a  few  drops  of  the  alcoholic  solution  are  added 
to  distilled  water.  No  rule  as  to  exact  proportions  can  be  given,  as 
these  depend  upon  the  material,  the  fixation,  and  the  intensity  of 
stain  desired. 

II.  Plasma  Dyes. — (a)  Eosin. 

This  is  prepared  as  follows  :  Water-soluble  eosin  is  dissolved  in 
water  to  saturation.  It  is  then  precipitated  by  hydrochloric  acid 
and  the  precipitate  washed  with  water  upon  a  filter  until  the  filtrate 
is  tinged  with  eosin.  After  drying,  the  precipitate  is  dissolved  in 
strong  alcohol,  1  gm.  of  eosin  to  1,500  c.c.  of  alcohol.  This  is  a 
rapid  plasma  stain. 

(/>)   Neutral  Carmine. 

Carmine .      1  gm. 

Liquor  ammonii  caustici    5  c.c. 

Distilled  water    50  c.c. 

The  last  two  ingredients  are  first  mixed,  and  the  carmine  then 
added.  This  solution  is  allowed  to  remain  in  an  open  vessel  for 
about  three  days,  or  until  the  odor  of  ammonia  has  disappeared,  after 
which  it  is  filtered. 

(r)  Acid  Aniline  Dyes. — Of  these  acid  fuchsin,  erythrosin,  and 
orange  G  are  most  used.  They  may  be  prepared  and  kept  in  stock 
in  the  same  manner  as  the  basic  aniline  dyes  (see  above).  Ery- 
throsin is  of  especial  value  for  sections  which  take  the  eosin  stain 
poorly. 


16  HISTOLOGICAL    TECHNIC. 

Staining  Sections. 

It  is  often  of  advantage  to  stain  the  different  tissue  elements 
different  colors.  This  may  be  accomplished  either  by  staining  suc- 
cessively with  several  dyes,  or  by  a  single  staining  with  a  mixture 
of  dyes.     The  following  are  the  methods  in  most  common  use : 

(i)  Staining  Double  with  Hematoxylin  and  Eosin. — Sec- 
tions are  first  washed  in  water.  They  are  then  stained  with  haema- 
toxylin  (solutions  I,  2,  4,  or  5,  pp.  13,  14)  from  three  to  ten  min- 
utes. After  being  thoroughly  washed  in  water,  they  are  dehydrated 
in  strong  alcohol  and  transferred  to  the  alcoholic  eosin  solution  (page 
15).  Most  sections  stain  in  from  two  to  five  minutes.  P>y  this 
method  nuclei  are  stained  blue  or  purple,  cell  bodies  and  intercellular 
substances,  red. 

(2)  Staining  with  Picro-Acid  Fuchsin. 

Acid  fuchsin,  i-per-cent  aqueous  solution 5  c.c. 

Picric  acid,  saturated  aqueous  solution 100  c.c. 

This  solution  usually  stains  in  from  one  to  three  minutes.  Occa- 
sionally a  longer  staining  is  required.  Cell  bodies  including  muscle 
cells  and  fibres  are  stained  yellow  by  the  picric  acid,  connective-tis- 
sue fibres  red  by  the  fuchsin.  After  staining,  the  sections  are 
washed  thoroughly  in  several  alcohols. 

(3)  Triple  Staining  with  Hematoxylin  and  Picro-Acid 
Fuchsin. — This  is  the  same  as  the  preceding  except  that  before 
staining  with  picro-acid  fuchsin,  the  sections  are  overstained  in 
hematoxylin  (solutions  1,  2,  4,  or  5,  pp.  13,  14).  The  usual  pur- 
ple of  hsematoxylin-stained  nuclei  is  changed  to  brown  by  the  action 
of  the  picric  acid.  Care  should  be  taken  that  the  sections  do  not 
remain  too  long  in  the  picro-acid  fuchsin,  or  the  hematoxylin  may 
be  completely  removed.  After  staining,  sections  are  washed  thor- 
oughly in  several  alcohols. 

If  sections  overstain  with  fuchsin,  the  staining  solution  may  be 
diluted  with  water;  if  sections  are  understained  with  fuchsin,  more 
fuchsin  may  be  added.  If  the  picric-acid  stain  is  not  sufficiently 
intense,  the  alcohol  in  which  the  sections  are  subsequently  washed 
should  be  tinged  with  picric  acid. 

(4)  Staining  with  Picro-Carmine. 

Ammonium  carminate 1  gm. 

Distilled  water 35  c.c. 

Picric  acid,  saturated  aqueous  solution       15  c.c. 


GENERAL    TECH  NIC.  17 

The  ammonium  carminate  is  first  dissolved  in  the  water,  after 
which  the  saturated  aqueous  solution  of  picric  acid  is  added  with 
constant  stirring.  The  mixture  is  then  allowed  to  stand  in  an  open 
vessel  for  two  days,  when  it  is  filtered.  This  fluid  stains  nuclei  and 
connective  tissue  red,  cell  protoplasm  yellow. 

Staining  in  Bulk. 

By  this  is  meant  the  staining  of  blocks  of  tissue  before  cutting 
into  sections.  The  method  is  much  less  used  than  formerly.  It  is 
slower  than  section  staining  and  more  difficult  to  control.  Blocks 
of  the  hardened  tissue  are  transferred  to  the  stain  from  water  or 
alcohol  according  to  the  solvent  of  the  stain.  Alum-carmine  and 
borax-carmine  are  the  most  used  general  bulk  stains. 

(1)  Alum-Carmine. 

Carmine 0.5  to  1  gm. 

Ammonia  alum,  4-per  cent  aqueous  solution  ...    ....  100  c.c. 

After  mixing  the  ingredients  the  solution  should  be  boiled  fifteen 
minutes,  and  after  cooling,  enough  sterile  water  added  to  replace  that 
lost  by  evaporation.  The  time  required  for  staining  depends  upon 
the  size  of  the  specimen.  There  is,  however,  little  danger  of  over- 
staining.  After  washing  out  the  excess  of  stain  with  water  the  spec- 
imen is  dehydrated  and  embedded  in  the  usual  way. 

(2)  Borax-Carmine,  Alcoholic  Solution. 

Carmine 3  gm. 

Borax 4gm. 

Water 93  c.c. 

After  mixing  the  above,  add  100  c.c.  70-per-cent  alcohol,  allow  the  mixture 
to  settle  ;  then  filter. 

About  twenty-four  hours  is  required  to  stain  blocks  0.5  cm.  in 
diameter.      Larger  blocks  require  longer  staining. 

IX.  Mounting. 

It  is  often  desirable  to  make  permanent  preparations  or  "mounts" 
of  the  stained  specimens. 

The  most  satisfactory  media  for  mounting  specimens  are  glycerin 
and  Canada  balsam. 

(1)  Glycerin. — Sections  may  be  transferred  to  glycerin  from 
either  water  or  alcohol.      In  the  case  of  double-stained  specimens — 


1 8  HISTOLOGICAL    TECHNIC. 

haematoxylin-eosin — the  glycerin  should  be  tinged  with  eosin,  as  the 
pure  glycerin  abstracts  the  eosin  from  the  tissues.  In  many  cases 
satisfactory  eosin  staining  may  be  obtained  by  simply  placing  the 
haematoxylin-stained  specimens  in  glycerin  strongly  tinged  with 
eosin  (eosin-glycerin).  The  specimen  in  a  drop  of  glycerin  is  trans- 
ferred to  the  glass  mounting  slide,  the  excess  of  glycerin  removed 
with  filter  paper  or  with  a  pipette  and  a  cover-glass  applied. 

Glycerin  mounts  must  be  cemented  to  exclude  air.  A  satisfac- 
tory cement  is  gold-size,  or  a  thick  solution  of  gum  shellac  in  alcohol 
to  which  a  little  castor  oil  has  been  added. 

Both  cover-glass  and  slide  must  be  cleaned  free  from  glycerin 
before  the  cement  is  applied.  A  camel's-hair  brush  is  used,  and  a 
ring  of  cement  is  painted  around  the  cover  in  such  a  manner  as  to 
seal  the  cover  to  the  slide. 

(2)  Balsam. — This  is  the  most  satisfactory  general  mounting 
medium.  It  has  an  advantage  over  glycerin  in  drying  down  perfectly 
hard  and  thus  needing  no  cement,  and  in  preserving  colors  more 
permanently.  Its  disadvantage  is  that  its  refractive  index  is  so  high 
that  it  sometimes  obscures  the  finer  details  of  structure,  especially  of 
unstained  or  slightly  stained  specimens. 

Specially  prepared  Canada  balsam  is  dissolved  either  in  xylol  or 
in  oil  of  cedar,  the  solution  being  made  of  any  desired  consistence. 
Xylol  balsam  dries  much  more  quickly  than  does  the  oil-of-cedar 
balsam. 

Preparatory  to  mounting  in  balsam,  stained  sections  must  be 
thoroughly  dehydrated  and  then  passed  through  some  medium  which 
is  miscible  with  both  alcohol  and  balsam.  This  medium,  which  at 
the  same  time  renders  the  section  transparent,  is  known  as  a  clearing 
medium.      For  celloidin  specimens  the  most  satisfactory  are  : 

(i)   Oil  of  origanum  cretici. 

(2)  Carbol-xylol  (xylol,  100  c.c.  ;  carbolic  acid  crystals,  22  gm.), 
followed  by  pure  xylol. 

(3)  Xylol  and  cajeput  oil,  equal  parts. 

After  clearing,  the  section  is  transferred  by  means  of  a  section- 
lifter  to  a  glass  mounting  slide.  It  is  then  blotted  firmly  with  filter 
paper  to  remove  the  excess  of  oil.  Care  must  be  taken  to  have  the 
filter  paper  several  layers  thick  in  order  that  the  oil  may  be  com- 
pletely removed.  The  specimen  should  also  be  blotted  firmly,  giv- 
ing the  oil  time  to  soak  into  the  paper.     These  two  precautions  are 


GENERAL    TECHNIC.  19 

necessary  to  prevent  the  section  adhering  to  the  paper  instead  of  to 
the  slide. 

After  blotting,  a  drop  of  balsam  is  placed  upon  the  centre  of  the 
specimen  and  a  cover-glass  applied. 

Paraffin  Sections. — The  technic  of  staining  and  mounting  paraffin 
sections  differs  from  that  of  celloidin  sections.  This  is  due  mainly 
to  the  fact  that  while  celloidin  is  transparent  and  may  remain  per- 
manently in  the  specimen,  paraffin  is  opaque  and  must  be  dissolved 
out  before  the  section  is  fit  for  microscopic  study. 

Bulk  staining  with  carmine  (page  17)  is  frequently  used  for 
specimens  which  are  to  be  embedded  in  paraffin.  Sections  may  be 
counter-stained  if  desired. 

The  following  are  the  steps  to  be  followed  in  staining  and  mount- 
ing paraffin  sections  : 

1 .    To  attach  sections  to  slide  : 

Place  a  drop  of  egg  albumen  (equal  parts  white  of  egg  and 
glycerin  to  which  a  little  carbolic  acid  may  be  added  for  preserving) 
on  a  slide,  and  spread  it  out  thin  with  the  finger. 

Place  a  few  drops  of  distilled  water  on  the  slide. 

Float  sections  on  the  water. 

Warm  gently  to  allow  sections  to  flatten— must  not  melt  paraffin. 

Pour  off  excess  of  water,  holding  the  end  of  the  ribbons  to  pre- 
vent them  floating  off. 

Stand  slides  on  end  in  water-bath  twelve  to  twenty-four  hours 
to  evaporate  water. 

2.  To  remove  paraffin  : 

Place  slide  in  xylol  three  to  five  minutes. 

3.  To  stain  sections : 

Place  slide  in  fresh  xylol  three  minutes. 
Transfer  to  absolute  alcohol. 
Transfer  to  90-per-cent  alcohol. 
Transfer  to  80-per-cent  alcohol. 
Transfer  to  50-per-cent  alcohol. 
Transfer  to  distilled  water. 
Stain  with  any  aqueous  stain. 
Wash  in  water. 

Transfer  to  50-per-cent  alcohol. 
Transfer  to  80-per-cent  alcohol 


20  HISTOLOGICAL    TECHNIC. 

Transfer  to  90-per-cent  alcohol. 

Transfer  to  absolute  alcohol. 

Transfer  to  xylol. 

Mount  in  xylol-balsam. 

If  an  alcohol  stain  is  used  instead  of  an  aqueous  one,  the  carrying 
down  and  up  through  the  graded  alcohols  may  be  omitted. 

If  it  is  desired  to  stain  double  with  eosin-haematoxylin  (page  16) 
use  the  above  technic,  the  hematoxylin  being  jhe  stain.  The  alco- 
holic eosin  stain  is  used  before  final  transfer  to  absolute  alcohol. 

X.  Injection. 

For  the  study  of  the  distribution  of  the  blood-vessels  in  tissues 
and  organs,  it  is  often  necessary  to  make  use  of  sections  in  which 
the  blood-vessels  have  been  injected  with  some  transparent  coloring 
matter.  The  injecting  fluid  most  commonly  used  is  a  solution  of 
colored  gelatin. 

The  gelatin  solution  is  prepared  by  soaking  1  part  gelatin  in  from 
5  to  10  parts  water — the  proportion  depending  upon  the  consistence 
desired — and  when  soft,  melting  on  a  water-bath. 

Various  dyes  are  used  for  coloring  the  gelatin,  the  most  common 
being  Prussian  blue  and  carmine. 

Prussian  blue  gelatin  is  prepared  by  adding  saturated  aqueous 
solution  Prussian  blue  to  the  gelatin  solution,  the  proportions  de- 
pending upon  the  depth  of  color  desired.  Both  solutions  should  be 
at  a  temperature  of  6o°  C.  After  thoroughly  mixing,  the  blue  gela- 
tin is  filtered  through  cloth. 

Carmine  gelatin  is  prepared  by  first  dissolving  1  gm.  carmine 
in  30  c.c.  distilled  water.  To  this  is  added  ammonia  until  the  mix- 
ture becomes  a  dark  cherry  red.  A  10-per-cent  aqueous  solution  of 
acetic  acid  is  next  added,  drop  by  drop,  with  constant  stirring  until 
the  mixture  becomes  neutral.  The  carmine  and  gelatin  solutions, 
both  being  at  about  60  °  C.,are  now  mixed  in  the  desired  proportions. 
If  the  carmine  injection  mass  is  alkaline,  it  diffuses  through  the 
walls  of  the  vessels;  if  acid,  there  is  a  precipitation  of  the  carmine 
which  may  interfere  with  its  free  passage  through  the  capillaries. 
If,  however,  the  alkaline  carmine  and  gelatin  be  first  mixed,  and  the 
10-per-cent  acetic  acid  solution  be  then  added  as  directed  above,  the 
precipitated  granules  are  so  fine,  even  with  an  acid  reaction,  that  they 
readily  pass  through  the  capillaries.      The  precipitation  of  the  car- 


GENERAL    TECHNIC.  21 

mine  in  the  shape  of  coarser  granules  is  of  advantage  when  it  is 
desired  to  have  an  injection  mass  which  will  fill  the  arteries  or  veins 
only,  without  passing  over  into  the  capillaries. 

The  injecting  apparatus  consists  of  a  vessel  which  contains  the 
injection  mass,  and  some  means  of  keeping  the  latter  under  a  con- 
stant but  easily  varied  pressure.  With  the  vessel  is  connected  a  tube 
ending  in  a  cannula,  through  which  the  injection  is  made. 

A  very  simple  apparatus  consists  of  a  shelf  which  can  be  raised 
and  lowered,  and  upon  which  the  vessel  stands.  The  tube  connect- 
ing with  the  cannula  may  be  attached  to  a  faucet  in  the  vessel  or  to 
a  bent  glass  tube  which  passes  into  the  top  of  the  vessel  and  acts  on 
the  principle  of  a  siphon. 

In  a  somewhat  more  elaborate  apparatus  the  injection  mass  is 
placed  in  a  closed  vessel,  and  this  is  connected  with  a  second  vessel 
containing  air  compressed  by  means  of  an  air  pump. 

Accurate  regulation  of  the  pressure  may  be  obtained  by  connect- 
ing the  injection  vessel  with  a  manometer. 

If  the  injection  is  to  occupy  considerable  time,  a  hot-water  bath 
in  which  the  gelatin  may  be  kept  at  an  even  temperature  is  also  nec- 
essary. 

Whole  animals  or  separate  organs  may  be  injected.  For  inject- 
ing a  whole  animal,  the  animal,  which  is  usually  a  small  one  such  as 
a  guinea-pig,  rat,  mouse,  or  frog,  is  chloroformed,  the  tip  of  the  heart 
is  cut  away  and  a  cannula  is  inserted  through  the  heart  into  the  aorta. 
This  is  first  connected  with  a  tube  leading  to  a  bottle  containing 
warm  normal  saline  solution.  Pressure  is  obtained  in  the  same 
manner  as  above  described  for  the  injection  mass.  By  this  means 
the  entire  arterial  and  venous  systems  are  thoroughly  washed  out 
until  the  return  flow  from  the  vena  cava  is  perfectly  clear.  The 
cannula  is  next  connected  with  the  tube  from  the  vessel  containing 
the  injection  mass,  the  pressure  being  only  sufficient  to  keep  the 
liquid  flowing.  When  the  injection  mass  flows  easily  and  freely 
from  the  vena  cava,  the  vessel  is  tied  and  the  pressure  is  increased 
slightly  and  continued  until  the  color  of  the  injection  mass  shows 
clearly  in  the  superficial  capillaries.  The  aorta  is  now  tied  and  the 
animal  immersed  in  cold  water  to  solidify  the  gelatin.  After  the 
gelatin  becomes  hard,  the  desired  organs  are  removed  and  fixed  and 
hardened  in  the  usual  way.  Sections  of  injected  material  are  usuall) 
cut  rather  thick,  that  the  vessels  may  be  traced  the  greater  distance 


22  HISTOLOGICAL    TEC ff NIC. 

Better  results  are  frequently  obtained  by  injecting  separate  organs. 
This  is  accomplished  by  injecting  through  the  main  artery  of  the 
organ  {e.g.,  the  lungs  through  the  pulmonary,  the  kidney  through  the 
renal).  The  injection  is  best  done  with  the  organ  in  situ,  although 
it  may  be  accomplished  after  the  organ  has  been  removed.  The 
method  is  the  same  as  given  above  for  injecting  an  animal  in  toto. 

The  so-called  double  injection  by  means  of  which,  an  attempt  is 
made  to  fill  the  arteries  with  an  injection  mass  of  one  color  (red), 
while  the  veins  are  filled  with  an  injection  mass  of  another  color 
(blue)  often  gives  pretty,  but  usually  inaccurate  pictures,  it  being 
as  a  rule  impossible  to  confine  each  injection  mass  to  one  system. 
Double  injection  is  accomplished  by  first  washing  out  the  vessels 
with  normal  saline  and  then  connecting  the  artery  with  the  red  gela- 
tin, the  vein  with  the  blue  gelatin,  and  injecting  both  at  the  same 
time,  the  pressure  driving  the  saline  out  of  the  vessels  into  the  tis- 
sues. The  difficulty  is  that  either  the  arterial  injection  carries  over 
into  the  veins,  or  the  venous  injection  carries  over  into  the  arterfes. 
A  somewhat  more  accurate  method  is  first  to  inject  the  veins  with  an 
injection  mass  in  which  the  coloring  matter  is  in  the  form  of  granules 
too  large  to  pass  through  the  capillaries,  and  then  to  inject  the  arte- 
ries and  capillaries  in  the  usual  manner.  This  method  is  especially 
useful  in  demonstrating  the  vessels  of  the  kidney,  liver,  and  gastro- 
intestinal canal. 


CHAPTER   II. 
SPECIAL   STAINING    METHODS. 

Of  these  only  the  more  common  will  be  described. 

(i)  Silver  Nitrate  Method  of  Staining  Intercellular 
Substance. — After  first  washing,  the  tissue,  e.g.,  omentum  or  cornea, 
is  placed  in  a  from  0.2  to  1  per  cent  solution  of  silver  nitrate,  where 
it  is  kept  in  the  dark  for  a  half-hour  or  more  according  to  the  thick- 
ness and  density  of  the  tissue.  The  specimen  is  then  washed  in 
water,  transferred  to  80-per-cent  alcohol  and  placed  in  the  direct 
sunlight  until  it  assumes  a  light  brown  color.  It  is  then  placed 
in  fresh  80-per-cent  alcohol  for  preservation. 

(2)  Chlorid  of  gold  in  1  -per-cent  aqueous  solution  is  used  in 
the  same  manner  for  demonstrating  connective-tissue  cells  and  their 
finer  processes. 

(3)  Weigert's  Elastic  Tissue  Stain. — This  is  prepared  as 
follows  : 

Fuchsin 2  gra. 

Resorcin 4  gm  • 

Water 200  c.c. 

These  are  boiled  for  five  minutes,  during  which  25  c.c.  of  liquor 
ferri  sesquichlorati  are  stirred  in.  The  result  is  a  precipitate  which 
should  be  filtered  out  after  the  liquid  has  become  cool.  After  dry- 
ing, 200  c.c.  of  95 -per-cent  alcohol  are  added  to  the  filtrate  and 
boiled  until  the  latter  dissolves.  Lastly,  4  c.c.  of  hydric  chlorid 
are  added  to  the  solution.  Sections  should  remain  in  the  stain 
thirty  minutes,  after  which  they  are  washed  in  alcohol  until  the  stain 
ceases  to  be  given  off. 

(4)  Golgi's  Chrome-Silver  Method  for  Demonstrating 
Secretory  Tubules. — Small  pieces  of  perfectly  fresh  tissue,  e.g., 
liver,  are  placed  in  the  following: 

Potassium  bichromate.  4-per-cent  aqueous  solution 4  vols. 

Osmic  acid,  1 -per-cent  aqueous  solution 1  vol. 

After  three  days  they  are   transferred   without  washing  to  a  0.75- 

23 


24  HISTOLOGICAL    TECHNIC. 

per-cent  aqueous  solution  of  silver  nitrate,  which  should  be  changed 
as  soon  as  a  precipitate  forms.  The  specimens  remain  in  the  second 
silver  solution  from  two  to  three  clays,  after  which  they  are  rapidly 
dehydrated,  embedded  in  celloidin,  and  cut  into  rather  thick  sections. 

(5)  Mallory's  Hematoxylin  Stain  for  Connective  Tissue. 
— Thin  sections  are  placed  for  from  two  to  ten  minutes  in  a  ten- 
per-cent  aqueous  solution  of  phosphomolybdic  acid.  They  are  then 
washed  in  distilled  water  and  transferred  to  : 

Phosphomolybdic  acid,  10-per-cent  aqueous  solution  .  100.0  c.c. 

Distilled  water 200.0  c.c. 

Hematoxylin  crystals 1.75  gm. 

Carbolic-acid  crystals    5.00  gm. 

The  phosphomolybdic  acid  and  water  are  first  mixed,  after  which 
the  hasmatoxylin  and  carbolic  acid  are  added. 

After  staining  from  ten  to  twenty  minutes  the  sections  are 
washed  in  distilled  water,  placed  for  five  minutes  in  50-per-cent 
alcohol,  then  in  strong  alcohol,  cleared  in  xylol  and  mounted  in  xylol 
balsam. 

(6)  Osmic  Acid  Stain  for  Fat. — For  this  purpose  osmic  acid 
is  used  in  a  1 -per-cent  aqueous  solution.  The  method  is  especially 
useful  for  demonstrating  developing  fat,  fatty  secretions  (mammary 
gland),  and  fat  absorption  (small  intestine).  Very  small  bits  of  the 
tissue  are  placed  in  the  osmic-acid  solution  for  from  twelve  to  twenty- 
four  hours.  They  are  then  hardened  in  graded  alcohols,  embedded 
in  celloidin,  and  the  sections  mounted  in  glycerin. 

(7)  Jenner's  Blood  Stain. 

Water-soluble  eosin — Griibler,    1 -per-cent  aqueous  solu- 
tion     ...      100  c.c. 

.Methylene  blue — pure — Griibler,  i-per-cent  aqueous  solu- 
tion     100  c.c. 

M  ix,  and  after  standing  twenty-four  hours  filter.  The  filtrate  is  dried  at  65  C, 
washed,  again  dried  and  powdered. 

To  make  the  staining  solution,  0.5  gm.  of  the  powder  is  dissolved 
in  100  c.c.  pure  methyl  alcohol.  Blood  smears  stain  in  from  two  to 
five  minutes.  They  are  then  washed  in  water,  dried,  and  mounted 
in  balsam. 

This  solution  acts  as  a  fixative  as  well  as  a  stain. 


CHAPTER  III. 
SPECIAL    NEUROLOGICAL    STAINING    METHODS. 

Weigert's  Method  of  Staining  Medullated  Nerve  Fibres. 

Material  is  fixed  in  one  of  the  following  fluids : 

(a)   Miiller's  fluid  (page  5). 

(&)   Potassium  bichromate,  5 -per- cent  aqueous  solution. 

(c)   Formalin,  10-per-cent  aqueous  solution. 

{d)  Formalin,  1  volume;  potassium  bichromate,  5-per-cent  aque- 
ous solution,  9  volumes. 

In  Miiller's  fluid  or  in  plain  potassium  bichromate  solution  a 
hardening  of  from  ten  days  to  three  weeks  is  required ;  in  formalin 
or  formalin- bichromate  for  a  week  to  ten  days  is  sufficient.  The 
specimens  are  then  hardened  in  graded  alcohols,  embedded  in  cel- 
loidin,  and  sections  cut  in  the  usual  way.  Material  fixed  in  formalin 
should  be  placed  for  several  days  in  either  a  5-per-cent  aqueous 
solution  of  copper  bichromate  or  in  the  following : 

Chrome  alum 1  gra. 

Potassium  bichromate 3  gm. 

Water...    100  c.c. 

before  hardening  in  alcohol. 

Sections  from  material  fixed  in  any  of  the  chrome  salt  solutions 
are  placed  for  from  twelve  to  twenty-four  hours  in  a  saturated  aqueous 
solution  of  neutral  cupric  acetate  diluted  with  an  equal  volume  of 
water.  From  the  fact  that  it  forms  some  combination  with  the  tis- 
sue whereby  the  latter  is  enabled  better  to  take  up  the  stain  used, 
this  solution  is  known  as  a  mordant  and  the  process  as  mordanting. 

After  mordanting,  the  sections  are  washed  in  water  and  trans- 
ferred to  the  following  staining  fluid  : 

Hematoxylin  crystals 1  gm. 

Alcohol,  95  per  cent 10  c.c. 

Lithium  carbonate— saturated  aqueous  solution   .........  1  c.c. 

Water go  c.c. 

This  solution  must    either    be    freshly  made    before  using    or    the 

2.5 


26  HISTOLOGICAL    TECH  NIC. 

hematoxylin  may  be  kept  in  io-per-cent  alcoholic  solution,  the  lith- 
ium carbonate  in  saturated  aqueous  solution,  and  the  staining  fluid 
made  from  these  as  needed. 

Sections  remain  in  the  hematoxylin  solution  from  two  to  twenty- 
four  hours,  the  longer  time  being  required  for  staining  the  finer  fibres 
of  the  cerebral  and  cerebellar  cortices.  They  are  then  washed  in 
water  and  decolorized  in  the  following : 

Potassium  ferricyanid ...,       2.5  gm. 

Sodium  biborate   2.0  gm. 

Water   ... 300.0  c.c. 

While  in  the  decolorizer,  sections  should  be  gently  shaken  or 
moved  about  with  a  glass  rod  to  insure  equal  decolorization.  In  the 
decolorizer  the  sections  lose  the  uniform  black  which  they  had  on 
removal  from  the  hematoxylin.  They  remain  in  the  decolorizing 
fluid  until  the  gray  matter  becomes  a  light  gray  or  yellow  color,  in 
sharp  contrast  to  the  white  matter  which  remains  dark.  Sections 
are  then  washed  in  several  waters  to  remove  all  traces  of  decolorizer 
and  dehydrated  in  alcohol. 

Weigert-Pal  Method. — In  this  modification  of  the  Weigert 
method,  sections  are  mordanted  in  a  3-  to  5-per-cent  aqueous  solution 
of  potassium  bichromate  instead  of  in  the  copper  acetate  solution. 
After  rinsing  in  water  the  sections  are  stained  in  hematoxylin  as 
in  the  ordinary  Weigert  method.  They  are  then  washed  and  trans- 
ferred to  a  0.2 5-per-cent  solution  of  potassium  permanganate,  where 
they  remain  from  one-half  to  two  minutes,  after  which  they  are  again 
washed  and  placed  in  the  following: 

Oxalic  acid 1  gm. 

Potassium  sulphite ...        1  gm. 

Water 200  c.c. 

In  this  solution  differentiation  takes  place,  the  medullary  sheaths 
remaining  dark,  while  the  color  is  entirely  removed  from  the  rest  of 
the  tissue.  If  the  section  is  still  too  dark,  it  may  again  be  carried 
through  the  permanganate  and  oxalic-acid  solutions  until  sufficiently 
decolorized. 

All  formalin  fixed  material  is  best  stained  by  the  Weigert-Pal 
method.  An  intensification  of  the  stain,  especially  of  the  very  fine 
fibres,  may  sometimes  be  obtained  by  placing  the  sections  for  several 
minutes  in  a  o. 5-per-cent  aqueous  solution  of  osmic  acid  before  de- 
colorizing:. 


SPECIAL   NEUROLOGICAL   STAINING  METHODS.     27 

Golgi  Methods  of  Staining  Nerve  Tissue. 

The  Golgi  methods  in  most  common  use  at  present  are  the  fol- 
lowing: 

(1)  Golgi  Silver  Methods. —  (a)  Slow  Method. — Blocks  of  tis- 
sue are  placed  for  several  months  in  a  3-per-cent  aqueous  solution 
of  potassium  bichromate.  Small  pieces  of  the  tissue  are  then  trans- 
ferred to  a  0.75-per-cent  aqueous  solution  of  silver  nitrate,  where  they 
remain  for  from  one  to  three  days.  The  only  method  of  determining 
whether  the  tissue  has  been  sufficiently  long  in  the  bichromate  is  to 
try  at  intervals  small  bits  of  the  tissue  in  the  silver  solution  until 
a  satisfactory  result  is  secured. 

(b)  Rapid  Method. — Small  pieces  of  tissue,  2  to  4  mm.  thick, 
are  placed  in  the  following  solution  for  from  two  to  six  days,  the 
time  depending  upon  the  age  and  character  of  the  tissue,  the  tem- 
perature at  which  fixation  is  carried  on,  and  the  elements  which  it 
is  desired  to  impregnate  : 

Osmic  acid,  i-per-cent  aqueous  solution ...    1  part. 

Potassium  bichromate,  3.5-per-cent  aqueous  solution   ...   4  parts. 

As  a  rule,  the  longer  the  hardening  the  fewer  are  the  elements 
stained,  but  these  few  are  clearer.  Pieces  of  tissue  should  be  tried 
each  day  until  a  satisfactory  result  is  obtained.  Further  treatment 
is  the  same  as  described  in  the  slow  method. 

(c)  Mixed  Method.  Specimens  are  placed  in  the  bichromate 
solution  for  about  four  days,  then  from  one  to  three  days  in  the 
osmium-bichromate  mixture  (see  Rapid  Method),  after  which  they  are 
transferred  to  the  silver  solution  (see  Slow  Method). 

(d)  Formalin-bichromate  Method.  Tissues  are  placed  for  from 
two  to  six  days  in  the  following  solution  : 

Formalin     .. 10  to  20  parts. 

Potassium   bichromate,  3-per-cent   aqueous   solu- 
tion ...    90  to  So  parts. 

Subsequent  treatment  with  silver  is  the  same  as  in  the  previously 
described  method.  The  results  resemble  those  of  the  slow  method. 
The  specimens  maybe  kept  in  strong  alcohol.  The  method  is  satis- 
factory only  for  the  adult  cerebrum  and  cerebellum. 

(2)  Golgi  Bichlorid  Method. — Material  remains  for  several 
months    in    the    potassium    bichromate    solution    (see    Slow    Silver 


28  HISTOLOGICAL    TECHNIC. 

Method),  after  which  it  is  transferred  to  a  saturated  aqueous  solu- 
tion of  mercuric  chlorid  for  from  four  to  twelve  months  or  longer. 
The  degree  of  impregnation  must  be  determined  by  frequently  test- 
ing the  material. 

A  modification  of  the  bichlorid  method,  known  as  the  Cox-Golgi 
method,  often  gives  good  results.     The  following  fixing  solution  is 

used : 

Potassium  bichromate,  5-per-cent  aqueous  solution  ....  20  parts. 

Mercuric  chlorid,  5-per-cent  aqueous  solution 20  parts. 

Distilled  water 40  parts. 

After  mixing  the  above,  add 

Potassium  chromate,  5-per-cent  aqueous  solution 16  parts. 

Tissues  remain  in  this  fluid  for  from  two  to  five  months. 

Golgi  specimens  should  be  dehydrated  and  embedded  as  rapidly 
as  possible.  This  is  especially  true  of  specimens  treated  by  the  rapid 
and  the  mixed  methods.  Those  treated  by  the  slow  silver  method 
and  by  the  bichlorid  method  are  more  permanent,  and  more  time 
may  be  taken  with  their  dehydration.  Sections  should  be  cut  thick 
(75  to  100, a)  and  mounted  in  xylol-balsam.  After  the  rapid  method, 
specimens  should  be  without  a  cover-glass ;  after  the  slow  method, 
specimens  may  be  mounted  with  or  without  a  cover.  The  balsam 
should  be  hard  and  melted  at  the  time  of  using  (see  Mounting, 
page  18). 

Nissl's  Method. 

This  method  is  useful  for  studying  the  internal  structure  of  the 
nerve  cell.  It  depends  upon  a  rapid  fixation  of  the  tissue,  its  sub- 
sequent staining  with  an  aniline  dye  and  final  decolorization  in 
alcohol. 

The  aniline  dye  most  commonly  used  is  methylene  blue.  There 
are  many  variations  and  modifications  of  Nissl's  method.  The  fol- 
lowing is  simple  and  gives  uniformly  good  results : 

Specimens  are  first  fixed  in  mercuric  chlorid  solution  (page  8), 
in  formalin  (10-per-cent  aqueous  solution),  or  in  absolute  alcohol, 
and  embedded  in  celloidin. 

Thin  sections  are  stained  in  a  i-per-cent  aqueous  solution  of 
pure  methylene  blue  (Grubler).  The  sections  are  gently  warmed  in 
the  solution  until  steam  begins  to  be  given  off.  They  are  then 
washed  in  water  and  differentiated  in  strong  alcohol,     The  degree  of 


SPECIAL  NEUROLOGICAL   STAINING  METHODS.     29 

decolorization  which  gives  the  best  results  can  be  learned  only  by 
practice.  Several  alcohols  must  be  used,  and  the  last  alcohol  must 
be  perfectly  free  from  methylene  blue.  The  sections  are  cleared  in 
equal  parts  xylol  and  cajeput  oil  and  mounted  in  xylol-balsam.  A 
contrast  stain  may  be  obtained  by  having  a  little  eosin  or  erythrosin 
in  the  last  alcohol. 

General  References  for  Further  Study  of  Technic. 

Lee:  The  Microtomist's  Vade-mecum. 
Mallory  and  Wright:  Pathological  Technique. 

Freeborn  :  Histological  Technic.     Reference  Handbook  of  Medical  Sciences, 
vol.  iv. 


PART  II. 
THE    CELL. 


CHAPTER  I. 


THE    CELL. 


In  the  simplest  forms  of  animal  life  the  entire  body  consists  of  a 
little  albuminous  structure,  the  essential  peculiarity  of  which  is  that 
it  possesses  properties  which  we  recognize  as  characteristic  of  living 
organisms.  This  albuminous  material  basis  of  life  is  known  as,  pro- 
toplasm, while  the  structure  itself  is  known  as  a  cell.     Within  the 


cell  membrane 


metaplasm  ! 
granules    f 

karyosome  or  | 
net-knob       S 


hyaloplasm 
spongioplasm 


linin  network 
nucleoplasm 


.    attraction-sphere 
"    centrosome 

~  plastids 

-*  chromatin  network 
--  nuclear  membrane 

--  nucleolus 
-    vacuole 


FIG.  i. — Diagram  of  a  Typical  Cell. 

cell  is  usually  found  a  specially  formed  part,  the  nucleus.  Peripher- 
ally some  cells  are  limited  by  a  distinct  cell  wall  ox  cell  membrane. 
An  actively  multiplying  cell  contains  a  minute  structure  associated 
with  the  reproductive  function  and  known  as  the  centrosome. 

A  typical  cell  thus  consists  of  the  following  structures  (Fig.  i)  : 
(i)  The  cell  body;  (2)  the  cell  membrane  ;  (3)  the  nucleus  ;  (4)  the 
centrosome.  Of  these  the  cell  body  is  the  only  one  present  in  all 
cells.  Most  animal  cells  have  no  cell  membrane.  A  few  cells  con- 
tain, in  their  fully  developed  condition,  no  nuclei.  In  many  mature 
cells  it  is  impossible  to  distinguish  a  centrosome. 

All  plants  and  animals  consist  of  cells  and  their  derivatives,  and 
if  an  attempt  be  made  to  resolve  any  of  the  more  complex  living 
3  33 


34 


THE  CELL. 


structures  into  its  component  elements,  it  is  found  that  the  smallest 
possible  subdivision  still  compatible  with  life  is  the  cell.  The  cell 
may  therefore  be  considered  as  the  histological  clement  or  unit  of 
structure. 

I.  The  Cell  Body  (protoplasm — cytoplasm). — This  is  a  semi-fluid 
substance  of  complex  chemical  composition,  belonging  to  the  general 
class  of  albumins.      It  contains  a  peculiar  nitrogenous  proteid,  plastin. 


Several  theories  are  held  as  to  the  ultimate  structure  of  proto- 
plasm (Fig.  2).      According  to  one  theory,  protoplasm  is  homogene- 
a  ous,  having  no  definite  struc- 

ture. Formerly  quite  generally 
accepted,  this  view  is  now  held 
by  but  few  cytologists. 

Other     investigators     con- 
sider  protoplasm  as    made  up 
of     (i)     a      fibrillar    element, 
which  may  occur  either  in  the 
form  of  a  network  of  anasto- 
mosing fibrils   (cytoreticulum) 
or  of  a  feltwork  of  independent 
fibrils    (filar  mass    or    miton), 
and    (2)   a    fluid   or   semi-fluid 
substance    which    fills    in   the 
meshes    of    the    reticulum    or 
separates  the  fibrils  (interfilar 
mass  or  paramiton)  (Fig.  2,  a). 
Altmann's  granule  theory 
considers   protoplasm   as  com- 
posed of  fine  granules  embed- 
ded in  a  gelatinous  intergran- 
ular    substance.     Altmann  believed  that  these  granules  represented 
the  ultimate  vital  elements,  and  for  this  reason  gave  them  the  name 
of  bioblasts  (Fig.  2,  />). 

According  to  Butchli,  protoplasm  is  a  foam  or  emulsion.  The 
appearance  of  a  reticulum  he  considered  due  to  the  fact  that  each  lit- 
tle foam  space  forms  a  complete  cavity  filled  with  fluid,  it  being  the 
cut  sides  of  these  spaces  which  give  the  reticular  appearance  on 
section  (Fig.  2,  c). 


Fig.  2.  —  Diagram  Illustrating  Theories  of  Proto- 
plasmic Structure,  a,  Fibrillar  theory;  £, 
granule  theory  ;  c,  "  foam  "  theory.  (The  gen- 
eral structure  of  cell  body  and  nucleus  corre- 
sponds.) 


The  formed  element  of  protoplasm,  whether  reticular  or  fibrillar 
in  structure,  is  known  as  spongioplasm,  the  homogeneous  element  as 
liyaloplasm  (Fig.  i).  Peculiar  bodies  known  as  plastids  (Fig.  i)  are 
of  frequent  occurrence  in  vegetable  cells,  but  are  also  found  in  some 


THE  CELL.  35 

animal  cells.  They  are  apparently  to  be  regarded  as  a  differentiation 
of  the  cytoplasm,  but  possess  a  remarkable  degree  of  independence, 
being  capable  of  subdivision  and  in  some  cases  of  existence  outside 
of  the  cell. 

Fat  droplets,  pigment  granules,  excretory  substances,  etc. ,  may 
be  present  in  cell  protoplasm.  These  bodies  represent  for  the  most 
part  either  food  elements  in  process  of  being  built  up  into  the  pro- 
toplasm of  the  cell  or  waste  products  of  cellular  activity.  To  such 
protoplasmic  "inclusions"  the  terms  deutoplasm,  paraplasm,  meta- 
plasm,  have  been  applied  (Fig.  i). 

When  the  protoplasm  of  a  cell  can  be  differentiated  into  a  cen- 
tral granular  area  and  a  peripheral  clear  area,  the  former  is  known  as 
endoplasm,  the  latter  as  cxoplasm.  When  the  exoplasm  forms  a 
distinct  limiting  layer,  but  blends  imperceptibly  with  the  rest  of  the 
protoplasm,  it  is  known  as  the  critsta. 

2.  The  Cell  Membrane  (Fig.  i). — This  is  present  in  but  few  ani- 
mal cells,  and  is  a  modification  of  the  peripheral  part  of  the  protoplasm. 
When  a  membrane  surrounds  the  cell,  it  is  known  as  the  pellicula , 
when  cells  lie  upon  the  surface,  and  only  the  free  surface  is  covered 
by  a  membrane,  it  is  known  as  the  cuticula. 

3.  The  Nucleus  (Fig.  1). — This  is  a  vesicular  body  embedded  in 
the  cytoplasm.  Its  size  and  shape  usually  correspond  somewhat  to  the 
size  and  shape  of  the  cell.  Considered  by  earlier  cytologists  an  unes- 
sential part  of  the  cell,  the  nucleus  is  now  known  to  be  most  inti- 
mately associated  with  cellular  activities.  It  is  not  only  essential 
to  the  carrying  on  of  the  ordinary  metabolic  processes  of  the  cell, 
but  is  an  active  agent  in  the  phenomena  of  mitosis,  which  in  most 
cases  determine  cell  reproduction. 

As  a  rule  each  cell  contains  a  single  nucleus.  Some  cells  con- 
tain more  than  one  nucleus,  as,  e.g.,  such  multinuclear  cells  as  are 
found  in  marrow  and  in  developing  bone.  Some  cells,  such  as  the 
human  red  blood  cell  and  the  respiratory  epithelium,  are,  in  their 
mature  condition,  non-nucleated.  All  non -nucleated  cells,  however, 
contained  nuclei  in  the  earlier  stages  of  their  development.  Non- 
nucleated  cells,  while  capable  of  performing  certain  functions,  are 
wholly  incapable  of  proliferation.  The  non-nucleated  condition 
must  therefore  be  regarded  as  not  only  a  condition  of  maturity 
but  of  actual  senility,  at  least  as  far  as  reproductive  powers  are 
concerned. 


36  THE  CELL. 

Chemically  the  nucleus  is  extremely  complex,  being  composed  of 
the  proteids  nuclein,  paranuclein,  linin,  nuclear  fluid,  and  lantanin. 

Morphologically  also  the  nucleus  is  complex,  much  of  the  struc- 
tural differentiation  being  determined  by  the  staining  reactions  of 
the  different  elements  when  treated  with  certain  aniline  dyes.  The 
nuclear  structures  and  their  relations  to  the  chemical  constituents  of 
the  nucleus  are  as  follows  : 

(/?)  The  nuclear  membrane  (amp hipy renin).  This  forms  a  limit- 
ing membrane  separating  the  nucleus  from  the  cell  protoplasm.  It 
is  wanting  in  some  nuclei. 

(It)  The  intranuclear  network,  or  nucleoreticulum,  consists  of  a 
chromatic  clement  (nuclein  or  chromatin)  and  of  an  acliromatic  cle- 
ment (linin).  At  nodal  points  of  the  network  there  are  often  consider- 
able accumulations  of  chromatin.  These  nodal  points,  at  first  thought 
to  be  nucleoli,  are  now  known  as  false  nucleoli,  or  karyosomes.  In- 
stead of  a  distinct  network  there  may  be  disconnected  threads  or  simply 
granules  of  chromatin.  Chromatin  is  the  most  characteristic  of  the 
chemical  constituents  of  the  nucleus  and  the  only  one  which  contains 
phosphoric  acid.  Within  the  linin  fine  granules  occur  (lantanin). 
These  are  differentiated  from  chromatin  by  the  fact  that  they 
are  most  susceptible  to  acid  dyes,  while  chromatin  takes  basic 
dyes. 

(c)  The  nucleolus  or  plasmosomc  (paranuclein-pyrenin)  is  a  small 
spherical  body  within  the  nucleus.  It  stains  intensely  with  basic 
dyes.      Its  function  is  unknown. 

(d)  Nucleoplasm  (karyoplasu/,  nuclear  fluid,  nuclear  sap).  This 
is  the  fluid  or  semi-fluid  material  which  fills  in  the  meshes  of  the 
nucleoreticulum. 

While  the  nucleus  is  a  perfectly  distinct  structure  and  is  usually 
separated  by  a  membrane  from  the  rest  of  the  cell,  a  marked  simi- 
larity exists  between  the  structure  of  nucleoplasm  and  cytoplasm. 
This  similarity  is  emphasized  by  the  absence  in  some  resting  cells 
of  any  nuclear  membrane,  by  the  apparent  direct  continuity  in  some 
cases  of  nucleoreticulum  and  cytoreticulum,  and  by  the  continuity  of 
nucleoplasm  and  cytoplasm  in  all  cells  during  cell  division. 

4.  The  centrosome  (Fig.  1)  is  a  small  spherical  body  found  some- 
times in  the  nucleus,  or  more  commonly  in  the  cytoplasm  near  the 
nucleus.  Surrounding  the  centrosome  there  is  usually  an  area  of  fine 
radiation  fibrils,  the  centrosphere  {attraction  sphere,  protoplasmic  ra- 


THE   CELL.  37 

diation,  and  arcJioplasvi).  The  main  significance  of  the  centrosome 
is  in  connection  with  cell  division,  under  which  head  it  will  be 
further  considered  (page  40). 

Vital  Properties  of  Cells. 

It  has  already  been  noted  that  the  essential  peculiarity  of  the  cell 
is  that  it  possesses  certain  properties  which  are  characteristic  of  life. 
By  this  is  meant  that  a  cell  is  able : 

1.  To  nourish  itself  and  to  grow — metabolism. 

2.  To  do  work  — function. 

3.  To  respond  to  stimulation — irritability. 

4.  To  move — motion. 

5.  To  produce  other  cells — reproduction. 

1.  Metabolism. — This  term  is  used  to  designate  those  cellular 
activities  which  have  to  do  with  the  nutrition  of  the  cell.  A  cell  is 
able  (1)  to  take  up  from  without  substances  suitable  for  its  nutrition 
and  to  transform  these  into  its  own  peculiar  structure,  and  (2)  to  dis- 
pose of  the  waste  products  of  intracellular  activities.  The  former  is 
known  as  constructive  metabolism  or  anabolism,  the  latter  as  destruc- 
tive metabolism  or  katabolism. 

2.  Function. — This  is  the  special  work  which  it  is  the  part  of 
the  cell  to  perform.  It  varies  greatly  for  different  cells.  Some  cells, 
as,  e.g.,  the  surface  cells  of  the  skin,  appear  to  act  mainly  as  protection 
for  more  delicate  underlyi  ng  structures.  Other  cells — gland  cells — 
in  addition  to  maintaining  their  own  nutrition  produce  specific  sub- 
stances (secretions),  which  are  of  great  importance  to  the  body  as  a 
whole.  Still  other  cells,  e.g.,  nerve  cells  and  muscle  cells,  have  the 
power  to  store  up  their  food  substances  in  such  a  way  as  to  make 
them  available  in  the  form  of  energy.  This  appears  to  be  accom- 
plished by  the  building  up  within  the  cell  of  highly  complex  and, 
consequently,  unstable  molecular  combinations.  By  reduction  of 
these  unstable  combinations,  molecules  of  greater  stability  and  less 
complexity  are  formed.  This  results  in  the  transformation  of  poten- 
tial into  kinetic  energy,  and  the  expenditure  of  this  energy  is  ex- 
pressed in  the  function. 

3.  Irritability  is  that  property  which  enables  a  cell  to  respond  to 
external  stimuli.  Cells  vary  in  respect  to  their  irritability,  the  most 
markedly  irritable  cells   in  higher  animals  being  those  of  the  neuro- 


38  THE   CELL. 

muscular  mechanism.  Stimulation  may  be  mechanical,  electrical, 
thermal,  chemical,  etc.  The  response  of  the  cell  to  certain  forms  of 
chemical  stimulation  is  known  as  chemotaxis.  Some  substances 
attract  cells  (positive  chemotaxis) ;  others  repel  cells  (negative  chemo- 
taxis).     Stimuli   other  than   chemical  possess  similar  properties,  as 


:"-:>..  "I 


FlG.  3. — Amoeboid  Movement.     Successive  changes  in  shape  and  position  of  fresh-water 

amoeba. 

indicated  by  the  terms  thermotaxis,  galvanotaxis,  etc.  Some  cells 
are  so  specialized  as  to  react  only  to  certain  kinds  of  stimulation, 
e.g.,  the  retinal  cells  only  to  light  stimuli. 

4.  Motion. — This  is  dependent  wholly  upon  the  protoplasm  of  the 
cell,  and  is  exhibited  in  several  somewhat  different  forms. 

(a)  Amoeboid  movement.  This  consists  in  the  pushing  outward 
by  the  cell  of  processes  (pseudopodia).  These  may  be  retracted  or 
may  draw  the  cell  after  them.  In  this  way  the  cell  may  change  both 
its  shape  and  position  (Fig.   3). 

(b)  Protoplasmic  movement.  This  occurs  wholly  within  the 
limits  of  the  cell,  changing  neither  its  shape  nor  position.  It  occurs 
in  both  plant  and  animal  cells,  and  consists  of  a  sort  of  circulation 
or  "  streaming  "  of  the  protoplasm.  It  is  usually  evidenced  by  the 
movement  of  minute  granules  present  in  the  protoplasm,  by  changes 
in  the  position  of  the  nucleus,  etc. 

(c)  Ciliary  movement.  This  is  the  whipping  motion  possessed 
by  little  hair-like  processes  called  cilia,  which  project  from  the  sur- 
faces of  some  cells. 

Certain  cells  which  are  specialized  for  the  particular  purpose  of 
motion,  as  e.g.  the  muscle  cell,  possess  such  powers  of  contraction 
that  they  are  able  to  move  not  only  themselves  but  other  parts  with 
which  they  are  connected.  This  power  of  contractility  is  dependent 
upon  the  spongioplasm,  the  hyaloplasm  playing  a  more  passive  role. 
In  muscle  cells  the  highly  developed  contractile  powers  appear  to  be 
due  to  the  excessive  development  and  peculiar  arrangement  of  the 
spongioplasm. 


THE  CELL. 


39 


5.  Reproduction. — The  overthrow  of  the  long-held  biological  fal- 
lacy of  spontaneous  generation  was  soon  followed  by  the  downfall  of 
a  similar  theory  regarding  the  origin  of  cells.  We  now  know  that 
all  cells  are  derived  from  cells,  and  that  the  vast  number  and  com- 
plex of  cells  which  together  form  the  adult  human  body  are  all  de- 
rived from  a  single  primitive  cell,  the  ovum. 

Reproduction  of  cells  takes  place  in  two  ways,  by  direct  cell  divi- 
sion or  amitosis,  and  by  indirect  cell  division  or  mitosis.  In  both 
amitosis  and  mitosis  the  division  of  the  cell  body  is  preceded  by 
division  of  the  nucleus. 

Direct  Cell-Division — Amitosis  (Fig.  4). — In  this  form  of 
cell-division  the  nucleus  divides  into  two  daughter  nuclei  without  any 
apparent  preliminary  changes  in  its  structure.  The  division  of  the 
nucleus  may  or  may  not  be  followed  by  division  of  the  cell  body. 
This  form  of  cell-division  is  uncommon  in  higher  animals  where 
Flemming  considers  it  a  degenerative  phenomenon  rather  than  a  nor- 
mal method  of  cell-increase.  It  is  a  common  method  of  cell-division 
in  the  protozoa. 

Indirect  Cell-Division — Mitosis  (Fig.  5). — In  this  form  of 
cell  division  also  the  nucleus  divides  into  two  daughter  nuclei,  but 
only  after  having  undergone 
certain  characteristic  changes 
in  structure.  On  account  of 
their  complexity  it  is  con- 
venient for  purposes  of  de- 
scription to  divide  these 
changes  into  stages  or  phases. 
Thus  we  recognize  in  mitosis 
(a)  the  prophase;  {b)  the 
metaphasc  ;  (c)  the  anaphase; 
(d)  the  telophase. 

(a)    The  Prophase  (Fig.  5, 

£j     C    ]J\         This    is    the  Sta°"e    FIG- 4-— Epithelial  Cells  from  Ovary  of  Cockroach. 

showing  Nuclei  dividing  Amitoticallv.     (Wheeler.) 

of  preparation  on  the  part  of 

the   nucleus  for  division.      It  is  marked   by  the  following  changes 

in  the  nucleus  : 

1 .  The  chromatic  part  of  the  intranuclear  network  becomes 
changed  into  a  twisted  skein  or  spireme.  This  is  formed  of  a  single 
long  thread  of  chromatin  or  of  several  shorter  threads  (Fig.  5,  B). 


40 


THE  CELL. 


2.  During  these  changes  in  the  network,  the  nucleolus  and  nuclear 
membrane  disappear  and  the  centrosome  and  its  surrounding  attrac- 
tion sphere  increase  in  size. 

3.  The  centrosome  next  divides  into  two  equal  parts.  These 
two  daughter  centrosomes,  each  surrounded  by  its  attraction  sphere, 
move  apart  but  remain  connected  by  fine  fibrils,  probably  derived 


FIG.  5.— Diagrams  of  Successive  Phases  of  Mitosis. 

A,  Resting  cell,  with   reticular  nucleus  and   true   nucleolus;   c,  attraction  sphere   with  two 

centrosomes. 

B,  Early  prophase.      Chromatin    forming   continuous   thread  —  the   spireme;    nucleolus   still 

present  ;  a,  amphiaster  ;  the  two  centrosomes  connected  by  fibrils  of  achromatic  spindle. 
C\  Later  prophase.     Segmentation  of  spireme  to  form  the  chromosomes;  achromatic  spindle 

connecting  centrosomes  ;  polar  rays  ;  mantle  fibres  ;  fading  of  nuclear  membrane. 
/>.  End  of  prophase.     Monaster — mitotic  figure  complete;  ep,  chromosomes  arranged  around 

equator  of  nucleus  ;  fibrils  of  achromatic  spindle  connecting  centrosomes;  mantle  fibres 

passing  from  centrosomes  to  chromosomes. 


from  the  linin  (Fig.  5,  />').  These  fibrils  form  the  central  ox  achro- 
matic spindle.  Two  other  sets  of  fibrils  radiate  from  each  centrosome 
— one,  known  as  the  polar  rays,  passes  out  toward  the  periphery  of 
the  cell;  the  other,  known  as  the  mantle  fibres,  extends  from  the 
centrosome  to  the  chromosomes  (Fig.  5,  C). 

4.  The  spireme  next   breaks  up  into  a  number  of  segments — 


THE  CELL. 


41 


chromosomes  (Fig.  5,  C).  These  arrange  themselves  regularly  around 
the  equator  of  the  nucleus,  forming  loops,  the  closed  ends  of  which 
are  directed  centrally.  This  is  known  as  the  closed  skein,  mother 
star,  or  monaster  (Fig.  5,  D).  The  number  of  chromosomes  varies 
for  different  species  of  plants  and  animals,  but  is  fixed  and  charac- 
teristic for  a  given  species. 


FIG.  5.— Diagrams  of  Successive  Phases  of  Mitosis. 

E,  Metaphase.     Longitudinal  cleavage;  splitting  of  chromosomes  to  form  daughter  chromo- 

somes, ep  ;  n,  cast-off  nucleolus. 

F,  Anaphase.     Daughter  chromosomes   passing  along  fibrils    of  achromatic   spindle  toward 

centrosomes;  division  of  centrosomes  ;  if,  interzonal  fibres  or  central  spindle. 

G,  Late  anaphase.     Formation  of  diaster  ;  beginning  division  of  cell  body. 

H,  Telophase.     Reappearance  of  nuclear  membrane  and  nucleolus  ;  two  complete  daughter 
cells,  each  containing  a  resting  nucleus.    (E.  B.  Wilson,  "  The  Cell,"  The  Macmillan  Co.) 

(o)  Metaphase  (Fig.  5,  E).  This  marks  the  beginning  of  actual 
division  of  the  nucleus. 

Each  chromosome  splits  longitudinally  (longitudinal  cleavage) 
into  two  daughter  chromosomes. 

(c)  Anaphase  (Fig.  5,  F,  G). — An  equal  number  of  daughter 
chromosomes  now  travels  along  the  fibrils  of  the  achromatic  spindle 
— apparently  under  the  influence  of  the  mantle  fibres — toward  each 
daughter  centrosome.      In  this  way  are  formed  two  daughter  stars, 


42  THE  CELL. 

the  mitotic  figure  being  known  at  this  stage  as  the  diastcr  (Fig.  5,  G). 
These  daughter  stars  are  at  first  connected  by  the  fibrils  of  the  achro- 
matic spindle.  In  this  stage  may  also  occur  beginning  division  of 
the  cell  body. 

(d)  Telophase  (Fig.  5,  H). — This  is  marked  by  division  of  the  cell 
protoplasm  and  consists  of  a  cycle  of  changes,  by  means  of  which  each 
group  of  daughter  chromosomes  is  transformed  into  the  chromatin 
network  of  a  resting  nucleus.  These  changes  are  the  same  as  those 
described  in  the  prophase,  but  occur  in  the  reverse  order,  the  chromo- 
somes uniting  to  form  the  spireme,  and  the  spireme  becoming  trans- 
formed into  the  nuclear  network.  The  result  is  the  formation  of 
two  daughter  cells.  The  nuclear  membrane  reappears,  as  does 
also  the  nucleolus.  Each  daughter  cell  is  thus  provided  with  a  rest- 
ing nucleus. 

It  is  through  the  above-described  process  of  cell-division  that  the 
vast  number  of  cells  which  make  up  the  adult  body  are  developed 
from  one  original  cell — the  ovum.  Such  powers  of  evolution  are 
not,  however,  inherent  in  the  ovum  itself,  but  are  acquired  only  after 
its  union  with  germinal  elements  from  the  male.  This  union  of  male 
and  female  germinal  elements  is  known  as  fertilization  of  the  ovum. 

Fertilization  of  the  Ovum. 

Prior  to  and  in  preparation  for  fertilization,  both  male  and  female 
cells  must  pass  through  certain  changes.  These  are  known  as  matu- 
ration of  the  spermatozoon  on  the  male  side  and  of  the  ovum  on  the 
female. 

The  spermatozoon  (Fig.  6)  is  developed  from  a  cell  of  the  seminifer- 
ous tubule  of  the  testis.  The  nucleus  of  this  cell  so  divides  its  chro- 
mosomes that  each  spermatozoon  contains  just  onc-lialf the  number  of 
chromosomes  characteristic  of  cells  of  the  species.  These  are  con- 
tained in  the  head  of  the  spermatozoon,  which  thus  represents  the 
nucleus  of  the  male  sexual  cell,  the  middle  piece  being  the  ccntro- 
somc,  the  tail  piece  the  remains  of  the  protoplasm. 

The  nucleus  of  the  ovum  or  germinal  vesicle  also  passes  through 
a  series  of  changes  by  which  it  loses  one-half  its  chromosomes. 
The  germinal  vesicle  or  nucleus  of  the  ovum  first  undergoes  mi- 
totic division  with  the  usual  longitudinal  cleavage  of  its  chromosomes 


THE  CELL. 


43 


and  the  formation  of  tzvo  daughter  nuclei.  One  of  these  and  its  cen- 
trosome  are  extruded  from  the  cell  as  the  first  polar  body.  The  re- 
maining nucleus  and  centrosome  again  divide  mitotically  only  in  this 
second  division,  instead  of  the  usual  longitudinal  cleavage  of  chro- 
mosomes, by  which  each  daughter  nucleus  is  provided  with  the  same 
number  of  chromosomes  as  the  mother  nucleus  :  the  chromosomes 
simply  separate,  one-half  going  to  each  datigJitcr 
nucleus.  One  of  the  daughter  nuclei  and  its  cen- 
trosome is  now  extruded  as  the  second  polar  body. 
The  polar  bodies  ultimately  disappear,  as  does  also 
the  centrosome  remaining  within  the  egg.  This 
leaves  in  the  now  matured  ovum  a  single  nucleus, 
which  is  known  as  the  female  pronucleus,  and 
which  contains  one-half  the  number  of  chromosomes 
characteristic  of  cells  of  the  species. 

During  this  process  in  some  animals — in  others 
after  its  completion — the  spermatozoon  enters  the 
ovum,  losing  its  now  useless  tailpiece.  The  head 
of  the  spermatozoon  becomes  the  male  projtucleus, 
while  the  middle  piece  becomes  a  centrosome. 
The  chromatin  of  the  male  next  becomes  ar- 
ranged as  chromosomes.  Male  and  female  pro- 
nuclei now  lose  their  limiting  membranes  and 
approach  each  other,  their  chromosomes  intermin- 
gling. As  each  pronucleus  contained  one-half  the 
number,  the  monaster  thus  formed  contains  the  full 
number  of  chromosomes  characteristic  of  the  species. 
Meanwhile  the  male  centrosome,  formed  from  the 
body  of  the  spermatozoon,  divides  into  two  daughter 
centrosomes.  These  with  their  radiating  fibrils  have  the  same 
arrangement  relative  to  the  monaster  of  mingled  male  and  female 
chromosomes,  already  described  under  mitosis.  By  longitudinal 
cleavage  of  these  chromosomes,  as  in  ordinary  mitosis,  two  sets  of 
daughter  chromosomes  are  formed.  Each  set  passes  along  the 
filaments  of  the  achromatic  spindle  to  its  centrosome.  Thus  is 
formed  the  diaster.  By  continuation  of  the  mitotic  process  two  new 
nuclei  are  formed,  each  nucleus  containing  the  number  of  chromo- 
somes characteristic  of  the  species,  and  each  being  made  up  equally 
of   male    and  female   chromosome  elements.      Thus    occurs  the  first 


Fig.  6.  — Human 
Spermatozoa.  (Af- 
ter Re  t  zi  u  s  .  )  /, 
Head  seen  on  flat  ; 
2,  head  seen  on 
edge  ;  k,  head  ;  m, 
body  ;  /,  tail ;  e,  end 
piece. 


44 


THE   CELL. 


division  of  the  fertilized  ovum  into  two  daughter  cells.  By  similar 
mitotic  processes  these  two  cells  become  four,  the  four  cells  become 
eight,  etc.      This  is  known  as  segmentation  of  the  ovum. 

The  earlier  generations  of  these  cells  are  morphologically  alike  and 


membrane  of 
"ovum 

nucleus  of 
"ovum 

.entering  sper- 
matozoon. 

protoplasm  of 
'  ovum  with 
deutoplasm 
granules 


„-»  female  pronucleus 


male  pronucleus 


female  pronu- 
cleus 


head  of  sper- 
matozoon with 
centrosonie 


centrosome 


\  ,.  chromosome  of  female 
pronucleus 


chromosome  of  male 
pronucleus 


centrosome 


chromosome 
,•>'  from  female 
pronucleus 


^__3/  •  •-'•  /  — 'chromosome 
from  male 
pronucleus 


-  —  centrosome 


Fig 


Diagram  of  Fertilization  of  the  Ovum.  (The  somatic  number  of  chromosomes  being 
four.)  (From  Bohm  and  von  Davidoff,  after  Boveri.) 
Ovum  surrounded  by  spermatoza,  only  one  of  which  is  in  the  act  of  penetration.  Tow- 
ard the  latter  the  protoplasm  of  the  ovum  sends  out  a  process;  2,  Head  of  spermato- 
zoon has  entered  ovum,  its  body  becoming  the  male  centrosome,  its  tail  having  disap- 
peared ;  3,  The  head  of  spermatozoon  has  become  the  male  pronucleus.  Male  and  female 
pronuclei  approach  each  other.  Between  them  is  the  (male)  centrosome  ;  4,  The  spiremes 
of  male  and  female  pronuclei  have  each  formed  two  chromosomes.  The  centrosome  has 
divided  ;  5,  Male  and  female  chromosomes  have  mingled  and  by  longitudinal  cleavage  (see 
Mitosis,  p.  39)  have  become  eight.  These  become  arranged  in  the  equatorial  plane  of 
the  ovum.  Mantle  fibres  extend  from  centrosomes  to  chromosomes;  6,  Division  of  the 
ovum  ;  two  daughter  cells,  each  containing  a  daughter  nucleus.  Each  daughter  nucleus 
contains  four  chromosomes,  two  derived  from  each  pronucleus. 


THE  CELL. 


45 


are  known  as  blastomeres.  Soon,  however,  these  cells  become  spread 
out  and  at  the  same  time  separated  into  two  primary  germ  /avers 
The  outer  of  these  is  known  as  the  ectoderm  or  epiblast,  the  inner  as 


SEGMENTA- 
TION   CAVITV. 


FIG.  S.-Secrmentation  of  the  Ovum.     (From  Gerrish,  after  van  Keneden.) 


^  TZ™ZlT  7£%*  fl0m  fil'St  diVisi°n  °f  fertilized  ™°  i  *<  fa»«.ll  stage ;  ,,  «  . 
toderm  ;*«««- tt?//j,  entoderm.  "y  germ  layers.     Outer  celts,  ex.- 


46  *   THE  CELL. 

the  entoderm  or  hypoblast.  Between  these  two  layers  and  derived 
from  them  a  third  layer  is  formed,  the  mesoderm  or  mesoblast. 
These  three  layers  constitute  the  blastoderm. 

TECHNIC. 

i.  Fresh  cells  may  be  studied  by  gently  scraping  the  surface  of  the  tongue, 
transferring  the  mucus  thus  obtained  to  a  glass  slide  and  covering  with  a  cover- 
glass. 

2.  Red  blood  cells  from  the  frog  are  prepared  as  follows  :  After  killing  the  frog 
the  heart  is  opened  and  the  blood  allowed  to  drop  into  a  tube  containing  Hayem's 
fluid  (sodium  chlorid  i  gm.,  sodium  sulphate  5  gm.,  mercuric  chlorid  0.5  gm.,  dis- 
tilled water  100  c.c).  After  shaking,  the  cells  are  allowed  to  settle  for  from  twelve 
to  twenty-four  hours.  The  fixative  is  then  replaced  by  water,  the  tube  again 
shaken,  the  cells  allowed  to  settle,  and  the  water  is  replaced  with  80-per-cent  alco- 


ectoderm 


'  .  t- ' 


mesoderm  Q;f£  v.    ^_        i'V/'.^,  .;  ■■-,~^r^rr^^0&  :V    -    nP  -  >-\ 

MM  '^  X     ■%&'■  V  :':    'M'%  $&  -     "    ^?"  S  't  $i  -^ 
entoderm.  rs^^a^vS:''    '''     '  ^  :  -T"  __    '_     ".'  _.   Oi  'V-  ^'"  ^    '  J""Q 


Fig.  9. — Two  Primary  Germ  Layers.    (From  McMurrich,  after  Bonnet.) 

hol  tinged  with  iodin.  After  from  twelve  to  twenty-four  hours  the  alcohol  is  de- 
canted and  the  tube  partly  tilled  with  alum-carmine  solution  (page  15).  About 
twenty-four  hours  usually  suffices  for  staining  the  nuclei.  The  alum-carmine  is 
then  poured  off  and  the  cells  well  shaken  in  water.  After  settling,  the  water  is 
replaced  by  glycerin,  to  which  a  small  amount  of  picric  acid  has  been  added.  In 
this  the  cells  may  be  permanently  preserved.  The  nuclei  are  stained  red  by  the 
carmine,  the  cytoplasm  yellow  by  the  picric  acid. 

3.  Surface  cells  from  the  mucous  membrane  of  the  bladder.  The  bladder  is 
removed  from  a  recently  killed  animal,  pinned  out  mucous  membrane  side  up  on  a 
piece  of  cork  and  floated,  specimen  side  down,  on  equal  parts  Midler's  fluid  and 
Ranvier's  alcohol  (technic  4,  p.  5,  and  a.  p.  4)  for  from  twenty-four  to  forty-eight 
hours.  The  specimen  is  then  washed  in  water  and  the  cells  removed  by  gently 
scraping  the  surface.  These  may  then  be  stained  and  preserved  in  the  same 
manner  as  the  preceding.  Cells  from  the  different  layers  should  be  studied  ;  also 
the  appearance  of  the  large  surface  cells  seen  on  flat  and  on  edge,  showing  pitting 
of  under  surface  by  cells  beneath. 

4.  Amoeboid  movement  may  be  studied  by  watching  fresh-water  amoebae  or 
white  blood  cells.  A  drop  of  water  containing  amoebae  is  placed  on  a  slide,  covered 
and  a  brush  moistened  with  oil  is  passed  around  the  cover  to  prevent  evaporation. 
The  activity  of  the  amoebae  may  be  increased  by  slightly  raising  the  temperature. 
An  apparatus  known  as  the  warm  stage  is  convenient  for  demonstrating  amoeboid 
movement.     A  drop  ol    blood,  human,  or,  better,  from  one  of  the  cold-blooded 


THE   CELL.  47 

animals,  may  be  used  for  the  study  of  amoeboid  movement  in  the  white  blood  cells. 
It  should  be  placed  on  a  slide,  covered,  and  immediately  examined  on  the  warm 
stage. 

5.  Ciliary  movement  is  conveniently  studied  by  removing  a  small  piece  of  the 
gill  of  an  oyster  or  mussel,  teasing  it  gently  in  a  drop  of  normal  salt  solution  and 
covering.  The  cilia  being  very  long,  their  motion  may  be  easily  studied,  especially 
after  it  has  become  slow  from  loss  of  vitality. 

6.  Mitosis.  The  salamander  tadpole  and  the  newt  are  classical  subjects  for 
the  study  of  cell-division.  The  female  salamander  is  usually  full  of  embryo  tad- 
poles in  January  and  February.  The  embryos  are  removed  and  fixed  in  Flem- 
ming"s  fluid  (technic  7,  p.  6),  after  which  they  may  be  preserved  in  equal  parts  of 
alcohol,  glycerin,  and  water.  Mitotic  figures  may  be  found  in  almost  any  of  the 
tissues.  Pieces  of  epidermis  from  the  end  of  the  tail,  the  parietal  peritoneum,  and 
bits  of  the  gills  are  especially  satisfactory.  If  the  newt's  tail  is  used,  it  should  be 
fixed  in  the  same  manner,  embedded  in  paraffin  and  cut  into  thin  sections.  These 
are  stained  with  Heidenhain*s  hematoxylin,  technic  3.  p.  14. 

Certain  vegetable  tissues,  such  as  the  end  roots  of  a  young,  rapidly  growing 
onion,  or  magnolia  buds  are  excellent  for  the  study  of  mitosis.  The  technic  is  the 
same  as  for  animal  tissues. 


General  References  for  Further  Study  of  the  Cell. 

Wilson  :  The  Cell  in  Development  and  Inheritance. 

McMurrich  :  The  Development  of  the  Human  Body. 

Minot:  Human  Embryology.     A  Laboratory  Text-book  of  Embryology. 

Hertwig  :  Die  Zelle  und  die  Gewebe. 


PART   III. 

THE  TISSUES. 


CHAPTER    I. 
HISTOGENESIS—CLASSIFICATION. 

Ectoderm,  mesoderm,  and  entoderm  (see  page  46)  are  known 
as  the  primary  layers  of  the  blastoderm.  They  differ  from  one 
another  not  only  in  position,  but  also  in  the  structural  characteristics 
of  their  cells.  The  separation  of  the  blastomeres  into  these  three 
layers  represents  the  first  morphological  differentiation  of  the  cells 
of  the  developing  embryo.  By  further  and  constantly  increasing 
differentiation  are  developed  from  these  three  primary  layers  all  tis- 
sues and  organs,  each  layer  giving  rise  to  its  own  special  group  of 
tissues.  The  tissue  derivations  from  the  primary  layers  of  the  blasto- 
derm are  as  follows  : 

Ectoderm. — (1)  Epithelium  of  skin  and  its  appendages — hair, 
nails,  sweat,  sebaceous  and  mammary  glands,  including  smooth  mus- 
cle of  sweat  glands. 

(2)  Epithelium  of  mouth  and  anus,  of  glands  opening  into  mouth 
and  enamel  of  teeth. 

(3)  Epithelium  of  nose  and  of  glands  and  cavities  connected  with 
nose. 

(4)  Epithelium  of  external  auditory  canal  and  of  membranous 
labyrinth. 

(5)  Epithelium  of  anterior  surface  of  cornea,  of  conjunctiva,  and 
of  crystalline  lens. 

(6)  Epithelium  of  male  urethra,  except  prostatic  portion. 

(7)  Epithelium  of  pineal  bodies  and  of  pituitary  body. 

(8)  Entire  nervous  system,  including  retina. 

Entoderm. — (1)  Epithelium  of  digestive  tract  excepting  mouth 
and  anus,  and  of  glands  connected  with  digestive  tract. 

(2)  Epithelium  of  respiratory  tract  and  of  its  glands. 

(3)  Epithelium  of  bladder,  ureters,  female  urethra,  and  of  prostatic 
portion  of  male  urethra. 

(4)  Epithelium  of  tympanum  and  of  Eustachian  tube. 

(5)  Epithelium  of  thyroid  and  of  Hassel's  corpuscles  of  thymus. 

51 


52  THE    TISSUES. 

Mesoderm. — This  layer  early  splits  into  three  sub-layers : 

Mesothclium. — The  cells  of  this  layer  form  tissues  resembling 
epithelium.  They  line  the  serous  membranes — pleura,  pericardium, 
and  peritoneum ;  form  the  epithelium  of  the  genito-urinary  system 
except  that  of  ureters,  bladder,  and  urethra ;  and  give  rise  to  striated 
and  heart  muscle. 

Mesenchyme. — From  the  cells  of  this  layer  are  derived  all  con- 
nective tissues ;  the  lymphatic  organs,  including  the  spleen ;  cells 
classed  as  "  endothelial  "  cells,  which  line  the  vascular  and  lymphatic 
systems ;  smooth  muscle  and  bone  marrow. 

Mesamccboici  Cells. — From  these  are  derived  the  red  and  the 
white  blood  cells. 

In  all  but  the  lowest  forms  of  animal  life  the  body  consists  of  an 
orderly  arrangement  of  many  kinds  of  cells.  From  the  cells  is  de- 
veloped a  substance  which  lies  outside  the  cells  and  is  known  as  in- 
tercellular substance.  The  association  of  a  particular  type  of  cell 
with  a  particular  type  of  intercellular  substance  is  known  as  a  tissue. 
The  character  of  a  tissue  depends  upon  the  character  of  its  cells,  of 
its  intercellular  substance,  and  their  relations  to  each  other.  Further 
differentiation  of  cells  and  intercellular  substance  within  a  particular 
tissue  gives  rise  to  various  sub-groups  of  the  tissue.  The  association 
of  two  or  more  tissues  for  the  performance  of  a  particular  function  is 
known  as  an  organ. 

A  scientific  classification  of  the  tissues  is  at  present  impossible. 

The  foregoing  list  of  tissue  derivations  shows  how  unsatisfactory 
is  any  attempt  at  classification  on  the  basis  of  histogenesis,  many  tis- 
sues which  are  morphologically  similar  being  derived  from  two  or 
even  all  three  of  the  blastodermic  layers. 

The  following  is  the  usual  classification  of  adult  tissues: 

(i)   Epithelial  tissues. 

(2)  Connective  tissues. 

(3)  Blood. 

(4)  Muscle  tissue. 

(5)  Nerve  tissue. 


CHAPTER    II. 

EPITHELIUM    (INCLUDING    MESOTHELIUM    AND 
ENDOTHELIUM). 

Histogenesis. — Epithelium  is  derived  from  all  three  of  the  pri- 
mary blastodermic  layers.  It  is  at  first  a  thin  membrane- like  struc- 
ture composed  of  a  single  layer  of  cells.  This  condition  may  persist 
or  new  cells  may  develop  between  the  older  cells  and  the  underlying 
connective  tissue,  thus  forming  epithelium  several  layers  of  cells  in 
thickness. 

General  Characteristics. — Epithelium  consists  almost  wholly  of 
cells.  The  intercellular  substance  is  merely  sufficient  to  attach  the 
cells  to  one  another  and  is,  consequently,  known  as  cement  sub- 
stance. In  some  instances  the  protoplasm  of  adjacent  epithelial  cells 
is  seen  to  be  even  more  closely  associated,  the  intervening  cement 
substance  being  bridged  over  by  delicate  processes  of  protoplasm 
which  pass  from  one  cell  to  another  and  are  known  as  "  intercellular 
bridges'''  (see  Fig.  14,  p.  57).  It  seems  probable  that  the  minute 
spaces  between  the  processes  serve  as  channels  for  the  passage  of 
food  (lymph)  to  the  cells.  The  surface  cells  of  epithelium  are  united 
by  continuous  cement  substance  in  which  there  are  apparently  no 
spaces.      In  this  way  escape  of  lymph  is  prevented. 

Epithelial  cells  vary  in  size  and  shape,  the  element  of  pressure 
being  a  frequent  determining  factor  as  regards  shape.  Their  proto- 
plasm may  be  clear,  finely  or  coarsely  granular,  or  pigmented.  Each 
cell  usually  contains  a  single  well-defined  nucleus.  Two  or  more 
nuclei  are  sometimes  present.  Some  epithelial  cells  are,  when  fully 
matured,  non- nucleated. 

When  epithelium  rests  upon  connective  tissue,  it  is  usually  sepa- 
rated from  the  latter  by  a  thin,  apparently  homogeneous  membrane 
known  as  the  basal  membrane  ox  membrana  propria.  Authorities 
differ  as  to  whether  this  membrane  is  of  connective-tissue  or  of  epi- 
thelial origin. 

Surface  epithelial  cells  frequently  have  thickened  free  borders  or 

53 


54  THE   TISSUES. 

C7iticuhu,  which  unite  to  form  a  continuous  membrane,  the  cuticidar 
membrane.  Striations  extend  from  the  cytoplasm  into  the  cuticulae. 
A  still  greater  specialization  of  the  surface  of  the  cell  is  seen  in  the 
ciliated  cell.  In  these  cells  fine  hair-like  projections — cilia — extend 
from  the  surface  of  the  cell. 

Some  epithelial  cells  show  important  changes  connected  with  their 
functional  activities.  An  example  of  this  is  seen  in  the  mucous  cell 
in  which  there  is  a  transformation  of  the  greater  part  of  the  cyto- 
plasm into  or  its  replacement  by  mucus. 

Epithelia  are  devoid,  as  a  rule,  of  both  blood  and  lymph  vessels. 
An  exception  to  this  is  the  stria  vascularis  of  the  cochlea.  Nerves, 
on  the  other  hand,  are  abundant. 

Classification. — Epithelia  may  be  classified  according  to  shape 
and  arrangement  of  cells  as  follows  : 

(i)  Simple  Epithelium.— (a)  Squamous;  (b)  columnar;  (c)  pseu- 
dostratified. 

(2)  Stratified  Epithelium. — (a)  Squamous;  (b)  transitional;  (c) 
columnar. 

Special  forms  of  the  above-mentioned  types  are  known  as :  (a) 
ciliated  epithelium ;  (b)  pigmented  epithelium ;  (c)  glandular  epi- 
thelium;   (a7)  neuro-epithelium. 

(3)  Mesothelium  and  Endothelium. 

1.  Simple  Epithelium. 

In  simple  epithelium  the  cells  are  arranged  in  a  single  layer. 

(a)  Simple  squamous  epithelium  consists  of  flat  scale-like  cells 
which  are  united  by  an  extremely  small  amount  of  intercellular  sub- 
stance. The  edges  of  the  cells  are  smooth  or  serrated.  Seen  on 
flat  they  present  the  appearance  of  a  mosaic.  Seen  on  edge,  the  cells 
appear  fusiform,  being  thickest  at  the  centre,  where  the  nucleus  is 
situated,  and  thinning  out  toward  the  periphery.  Simple  squamous 
epithelium  has  but  a  limited  distribution  in  man,  occurring  as  respi- 
ratory epithelium  in  the  lungs  (non-nucleated),  in  Bowman's  capsule 
of  the  kidney  glomeruli,  in  the  descending  arm  of  Henle's  loop  of 
the  uriniferous  tubule,  the  pigmented  cells  of  the  retina,  and  the 
posterior  surface  of  the  anterior  lens  capsule. 

(b)  Simple  columnar  epithelium  consists  of  a  single  layer  of  elon- 
gated cells.     The  bases  of  the  cells  are  usually  separated  from  the 


EPITHELIUM. 


55 


underlying  connective  tissue  by  a  basement  membrane.  The  nu- 
cleus is,  as  a  rule,  in  the  deeper  part  of  the  cell,  near  the  basement 
membrane.     Many  of    these  cells    have  prominent    thickened    free 


FlG.  io. — Simple  Squamous  Epithelium.  Section  of  cat's  lung,  stained  with  silver  nitrate. 
(Klein.)  The  outlines  of  the  non-nucleated  simple  squamous  epithelial  cells  are  shown 
bv  wavy  black  lines. 


borders  or  cuticulae.  This  form  of  epithelium  is  often  ciliated. 
When  the  height  of  the  cell  about  equals  its  other  dimensions,  the 
epithelium  is  called  cuboidal.  Simple  columnar  epithelium  lines 
the  gastro-intestinal  canal,  the  uriniferous  tubule  (excepting  the  de- 


^"'""V^f  --\-~-  *r--—  ,--    '   -'-•"-'     "-    -~~-  --    -i 


Fig.  n. — Simple  Columnar  Epithelium  from  Human  Small  Intestine. 

scending  arm  of  Henle's  loop),  simple  tubular  glands,  the  ducts  of 
some  compound  tubular  glands,  the  smaller  bronchi,  and  the  mem- 
branous and  penile  portions  of  the  male  urethra. 


56 


THE    TISSUES. 


In  simple  columnar  epithelium,  in  addition  to  the  single  row  of 
epithelial  cells,  there  are  found  lying  near  the  basement  membrane, 

between  the  bases  of  the  epithelial 
cells,  small,  spherical  or  irregular 
cells,  which  frequently  show  mi- 
tosis and  which  are  known  as  re- 
placing cells.     They  appear  to  de- 

FiG.12.-DiagramofPseudostratifledEPi-      veloP     into    columnar     epithelial 
theiium,  showing  Nuclei  situated  at  Dif-      cells  as  they  are  needed  to  replace 

ferent  Levels. 

older  cells. 
if)  Pseudostratified  epithelium  is  a  form  of  simple  columnar  epi- 
thelium, in  which,  from  crowding  of  the  cells,  the  nuclei  have  come 
to  lie  at  different  levels,  thus  giving  the  appearance  of  stratification. 


2.  Stratified    Epithelium. 

In  stratified  epithelium  the  cells  are  arranged  in  more  than  one 
layer. 

(a)  Stratified  squamous  epithelium  is  developed  from  simple 
epithelium  by  the  growth  of  new  cells  between  the  old  cells  and  the 


FLAT   SURFACE    CELLS 


-  i~-~f~?^i  -'*■'■ 


POLYHEDRAL    CELLS 


CUBOIDAL    CELLS 


BASEMENT    MEMBRANE 

SUBEPITHELIAL    CONNECTIVE 
TISSUE 


m 


y&*rs<f.K'£f???..^»ftrw     ■■:•  ■■■■)■  •  ■■■■:  :y4:»:;i:.:rr\;  ■  /.,.  .r ':.:;;.;■.■,  '.'■,'] 


.  ..;■.;.    -  -,  -        ■ 


i*IG.  13. — Stratified  Squamous  Epithelium  from  Human  Cornea.    X  400. 


underlying  connective  tissue.      It  consists  of  several  layers  of  cells 
which   vary  greatly  in   size  and  shape.     The  surface  cells  are  large 


EPITHELIUM. 


57 


c  o  y:^A 


\ 


\ 


and  flat.  Beneath  these  are  several  layers  of  polyhedral  cells,  with 
often  very  distinct  protoplasmic  intercellular  connections  ("  intercel- 
lular bridges,"  see  also  page  53).  The 
deepest  cells  are  columnar  or  cuboidal.  It 
is  thus  seen  that  in  stratified  squamous 
epithelium  only  the  surface  cells  are  squa- 
mous. This  form  of  epithelium  rests  upon 
a  more  or  less  distinct  basement  membrane, 
which  is  frequently  thrown  up  into  folds 
by  papillae  of  the  underlying  connective 
tissue.  Stratified  squamous  epithelium 
forms  the  surface  of  the  skin  and  of  mucous 
membranes  of  cavities  opening  upon  it, 
mouth  and  oesophagus,  conjunctiva,  external 
ear,  vagina,  and  external  sheath  of  hair 
follicle. 

(I?)    Transitional  epithelium  is  a  stratified   epithelium   composed 
of  from  three  to  six  layers  of  cells.      It  rests  upon  connective  tissue 


2"   '  -     "J  ■":;"    '   ■ 


■•••••.: 


Fig.  14.— Epithelial  Cells  from 
the  Stratum  Spinosum  of  the 
Human  Epidermis,  showing 
"Intercellular  Bridges." 
X  700.     (Szymonowicz.) 


.-    r    -  r~ 


jfii 


:■ 


j  '.-\,V-.A  f  ; 


FIG.  15. — Transitional  Epithelium  from  the  Human  Bladder.     X  400. 


•\A" ■  "•--.•JSsf"  ;       ■ '-  -''"cSSi'v  -**$LV-    J&SxS;.,    ,xS'>; 

«'KV  ,'•—'.  -mv    - 


FIG.  16. — Stratified  Columnar  Epithelium  from  the  Human  Male  Urethra.     X  400. 


free  from  papillae.     The  surface  cells  are  large  and  may  contain  two 
or  three  nuclei.     Their  free  surfaces  are  flat,  while  their  under  sur- 


58 


THE    TISSUES. 


faces  show  depressions  due  to  pressure  from  underlying  cells.     The 
cells  of   the  deeper   layers  are  polygonal,  or   irregularly  cuboidal. 


'■■■'■■■■  ':■--'  :"'■':'  ;>■;■'■     '  Si  '     il^Hsl 


>J  '•  rJ* 


Fig.  17.  -Stratified  Columnar  Ciliated  Epithelium  from  the  Human  Trachea.     X  400. 

This  form  of  epithelium  lines  the  bladder,  ureter,  pelvis  of  the  kid- 
ney and  prostatic  portion  of  male  urethra. 

U)  Stratified  Columnar  Epithelium.- — Only  the  surface  cells  are 
columnar,  the  deeper  cells  being  irregular  in  shape.  The  surface 
cells  frequently  send  long  processes  down  among  the  underlying 
cells.     The  free  surface  is  often  marked  by  a  well-developed  cuticula. 


§     ^pga 


m 


,"'• 

$$$(:<■: 


-      m 


■■   l">  ■>%    l- 


H    f   V  •■■■■ 


Fig.  18.— Isolated  Ciliated  Cells  and  Goblet  Cells  from  Dog's  Trachea.     X  700. 


Some  epithelia  of  this  type  are  ciliated.  Stratified  columnar  epithe- 
lium is  found  in  the  larynx,  nose,  palpebral  conjunctiva,  largest  of 
the  gland  ducts,  the  vas  deferens  and  part  of  the  male  urethra. 


EPITHELIUM. 


59 


Modified  Forms  of  Epithelium. 

(a)   Ciliated  Epithelium. — In  this  form  of  epithelium,  fine  hair-like 
processes — cilia — extend  from  the  surface  of  the  cell.     These  cilia 
vary  from  twelve  to  twenty-five  for  each  cell  and  may  be  short  as  in 
the  trachea  or  long  as  in  the  epididymis.     There  is  usually  a  well- 
defined   cuticula   from   which  the  cilia  appear  to 
spring.      According  to  Apathy,  the    cilia    extend 
through  the  cuticulse,  giving  to  the  latter  a  striated 
appearance  (Fig.   19).     Just  beneath  the  cuticula 
each  cilium  shows  a  swelling — the  basal  granule. 
Lenhossek  considers  these  granules  centrosomes. 
The   intracellular  extensions  of  the  cilia  converge 
toward  the  nucleus,  and  are  continuous  with  the 
reticular  or   fibrillar   structure  of    the   cell   body. 
The  motion  of  cilia  is  wave-like,  the  wave  always 


Fig.  19. 


Fig.  20. 


FiG.  19.  — Ciliated  Epithelial  Cell  from  Intestine  of  Mollusk  (Engelmann),  showing,  a,  cuti- 
cula, b,  basal  granules,  and  c,  intracellular  extensions  of  cilia. 

PIG.  20.  — Pigmented  Epithelial  Cells  from  the  Human  Retina  (X  350),  showing  different  de- 
grees of  pigmentation.  The  clear  spots  in  the  centres  of  the  cells  represent  the  unstained 
nuclei. 

passing  in  the  same  direction.  Various  explanations  of  ciliary 
motion  have  been  given.  The  most  plausible  is  that  it  is  due  to  the 
contractile  powers  of  the  spongioplasm. 

Cilia  are  confined  to  the  surface  cells  of  simple  columnar  and 
stratified  columnar  epithelium. 

Simple  columnar  ciliated  epithelium  occurs  in  the  smaller 
bronchi,  uterus,  Fallopian  tubes  and  central  canal  of  the  spinal 
cord. 


6o 


THE    TISSUES. 


Stratified  columnar  ciliated  epithelium  occurs  in  large  bronchi, 
trachea,  larynx,  nose,  Eustachian  tube,  vas  deferens  and  epididymis. 

(b)  Pigmented  Epithelium  consists  of  cells  the  cytoplasm  of 
which  contains  brown  or  black  pigment.  It  is  usually  present  in  the 
form  of  spherical  or  rod-like  granules.  Examples  of  it  are  seen  in 
the  pigmented  epithelium  of  the  retina  and  in  the  pigmented  cells  of 
the  deeper  layers  of  the  epidermis  in  colored  races  (Fig.  20). 

(e)  Glandular  Epithelium.  —  This  forms  the  essential  or  secreting 
element  of  glands  and  is  mostly  of  the  simple  cylindrical  variety. 
The  different  kinds  of  glands  and  their  epithelia  will  be  described 
among  the  organs. 

(d)  Neuro-epithelium.  —  This  is  a  highly  specialized  form  of 
epithelium  which  occurs  in  connection  with  the  end  organs  of  nerves, 
under  which  heading  it  will  be  described. 

3.   Mesothelium  and  Endothelium. 

While  recognizing  the  present  tendency  toward  considering  those 
tissues  formerly  classified  as  endothelium,  as  simple  squamous  epithe- 
lium, the  correctness  of  the  newer  classification  still  remains  sub 


Fig.  21.— Mesothelium  from  Oment.im  of  Dog  Treated  according  to  Technic  7,  p.  62.  X  350. 
Black  wavy  lines  indicate  the  intercellular  cement  substance.  The  mesothelial  cells 
cover  the  strands  of  connective  tissue,  the  fibres  of  the  latter  being  visible  through  the 
transparent  cell  bodies. 

judice  and,  so  long  as  this   is  the  case,  we  prefer  to  retain  the  cer- 
tainly much  more  convenient  classification  of  Minot,  which  coincides 


EPITHELIUM.  6 1 

with  his  subdivision  of  the  mesoblast.  According  to  this  classifica- 
tion, for  those  tissues  which  resemble  epithelium  in  structure  and 
which   are  derived  from   the  mesenchyme,  the  term   endothelium   is 


FIG.  22. — The  Endothelium  of  a  Small  Blood-vessel.    Silver  nitrate  stain.     X  350. 

retained.  The  term  mesothelium  is  used  for  those  tissues  which  re- 
semble epithelium  and  which  are  derived  from  the  mesothelium. 

Mesothelium  and  endothelium  are  similar  in  structure.  Each 
consists  of  thin  flattened  cells  with  clear  or  slightly  granular  proto- 
plasm and  bulging  oval  or  spherical  nuclei.  The  edges  of  the  cells 
are  usually  wavy  or  serrated.  The  cells  are  united  by  an  extremely 
small  amount  of  intercellular  "  cement "  substance,  which  is  usually 
indistinguishable  except  by  the  use  of  a  special  technic. 

Endothelium  forms  the  walls  of  the  blood  and  lymph  capillaries 
and  lines  the  entire  blood-vessel  and  lymph-vessel  systems. 

Mesothelium  lines  the  body  cavities — the  pleura,  the  pericardium 
and  the  peritoneum. 

TECHNIC. 

1.  Simple  Squamous  Epithelium. — That  of  the  lung  may  be  demonstrated  by 
injecting  with  silver  solution  (technic  1,  p.  23)  through  a  bronchus  and  then  im- 
mersing the  tissue  in  the  same  solution.  The  lungs  of  young  kittens  furnish  espe- 
cially satisfactory  material. 

2.  Simple  Columnar  Epithelium. — A  piece  of  small  intestine,  human  or  animal, 
is  pinned  out  flat  on  cork  and  fixed  in  formalin-Midler's  fluid  (technic  5,  p.  5). 
Sections  are  cut  perpendicular  to  the  surface,  stained  with  hematoxylin  and  eosin 
(technic  1.  p.  16)  and  mounted  in  glycerin,  tinged  with  eosin  (page  18).  Little 
elevations  known  as  villi  project  from  the  inner  surface  of  the  intestine.  These 
are  covered  by  a  single  layer  of  columnar  epithelial  cells.  The  cuticulae  and 
cuticular  membrane  are  usually  well  shown.  Among  the  simple  cylindrical  cells 
are  seen  large  clear  or  slightly  blue-stained  cells.  These  are  known  from  Uieir 
secretion  as  mucous  cells,  from  their  shape  as  goblet  cells,  and  are  classed  as 
modified  epithelium  of  the  glandular  type.  These  should  be  studied  in  their  va- 
rious stages  of  secretion,  from  the  cell  in  which  only  a  small  amount  of  mucus  is 
present,  near  the  outer  margin,  to  the  cell  whose  protoplasm  is  almost  wholly  re- 
placed by  mucus.  Some  cells  will  be  found  in  which  the  surface  has  ruptured  and 
the  mucus  can  be  seen  pouring  out  of  the  cell. 


62  THE   TISSUES. 

3.  Stratified  Squamous  Epithelium. — The  cornea  furnishes  good  material  for 
the  study  of  stratified  squamous  epithelium.  An  eye  is  removed  from  a  freshly 
killed  animal  and  the  cornea  cut  out  and  fixed  informalin-Miiller's  fluid.  Sections 
are  cut  perpendicular  to  the  surface,  and  treated  as  in  the  preceding.  The  cells 
are  laid  down  in  from  six  to  eight  layers.  The  oesophagus  may  be  used  instead  of 
the  cornea,  its  mucous  membrane  being  lined  by  a  somewhat  thicker  epithelium. 

4.  Transitional  Epithelium. — This  is  conveniently  studied  in  the  mucous  mem- 
brane of  the  bladder.     Technic  same  as  2.  p.  61. 

5.  Stratified  Columnar  Epithelium. — A  portion  of  trachea  from  a  recently 
killed  animal  is  treated  according  to  same  technic.  The  surface  cells  are  ciliated 
so  that  this  specimen  also  serves  to  demonstrate  that  type  of  modified  epithelium. 
Isolated  cells  or  clumps  of  cells  may  be  obtained  from  the  trachea  in  the  manner 
described  in  technic  3.  p.  46. 

6.  Pigmented  Epithelium. — Fix  a  freshly  removed  eye  in  formalin-Muller's 
fluid  (page  5).  After  hardening,  cut  transversely  and  remove  the  vitreous  and 
retina.  The  pigmented  cells  remain  attached  to  the  inner  surface  of  the  choroid, 
and  may  be  removed  by  gently  scraping.  They  may  be  preserved  and  mounted  in 
glycerin. 

7.  Mesothelium. — Part  of  the  omentum  of  a  recently  killed  animal  is  removed 
and  washed  in  water,  care  being  taken  not  to  injure  the  tissue  in  handling.  The 
water  is  then  replaced  by  a  1  to  500  aqueous  solution  of  silver  nitrate.  After  half 
an  hour  the  specimen  is  removed  from  the  silver,  washed  in  water,  transferred  to 
80-per-cent  alcohol  and  placed  in  the  sunlight  until  it  becomes  of  a  light  brown 
color.  It  is  then  preserved  in  fresh  So-per-cent  alcohol.  The  nuclei  may  be 
stained  with  hematoxylin  (stain  5.  p.  14).  The  specimen  should  be  mounted  in 
glycerin.  Wavy  black  lines  indicate  the  intercellular  cement  substance.  The 
nuclei  of  the  mesothelial  cells  are  stained  blue,  those  of  the  underlying  connective- 
tissue  cells  a  paler  blue.  It  must  be  borne  in  mind  in  studying  this  specimen  that 
the  strands  or  trabeculae  of  the  omentum  are  not  composed  of  mesothelium,  but  of 
fibrous  connective  tissue,  and  that  the  flat  mesothelial  cells  merely  lie  upon  the 
surface  of  the  connective-tissue  strands. 

8.  Endothelium  may  be  demonstrated  by  removing  the  bladder  from  a  recently 
killed  frog,  distending  it  with  air  and  subjecting  it  to  the  same  technic.  By  this 
means  the  intercellular  substance  of  the  endothelium  of  the  blood-vessels  of  the 
bladder  wall  is  stained  and  the  outlines  of  the  cells  are  thus  shown. 


CHAPTER    III. 
THE   CONNECTIVE    TISSUES. 

Histogenesis.  —  All  of  the  connective  tissues,  with  the  single 
exception  of  the  connective  tissue  peculiar  to  the  nervous  system 
(neuroglia),  are  developed  from  the  sub-layer  of  the  mesoblast  known 
as  the  mesenchyme. 

The  mesoderm  consists  at  first  wholly  of  round  or  polygonal  cells. 
With  the  division  of  the  mesoderm  into  its  three  sub-layers,  the  cells 
of  the  mesenchyme  gradually  become  more  and  more  separated  from 
one  another  by  the  interposition  of  a  fluid  intercellular  substance. 
This  intercellular  substance  is  a  product  of  the  cell  and  is  at  first 
homogeneous  or  granular.  The  appearance  presented  at  this  stage 
is  that  of  irregular,  branching,  anastomosing  cells,  lying  in  a  semi- 
fluid ground  substance.     This  is  embryonic  connective  tissue. 

With  further  changes  in  both  cells  and  intercellular  substance, 
but  mainly  in  the  latter,  embryonic  connective  tissue  differentiates 
to  form  the  adult  types  of  connective  tissue. 

General  CJiaracteristics. — A  characteristic  of  the  connective  tis- 
sues is  the  predominance  of  the  intercellular  substance.  In  this  re- 
spect the  connective  tissues  differ  markedly  from  epithelial  tissues. 
Moreover,  it  is  the  intercellular  substance  and  not  the  cells  which 
determines  the  physical  character  of  the  tissue.  The  division  of 
connective  tissue  into  its  various  sub-groups  is  also  based  upon  struc- 
tural differences  in  the  intercellular  substance. 

Classification. — The  connective  tissues  may  be  classified  as 
follows : 

i.   Fibrillar  connective  tissue,  including  areolar  tissue. 

2.  Elastic  tissue. 

3.  Embryonal  and  mucous  tissue. 

4.  Reticular  tissue. 

5.  Lymphatic  or  adenoid  tissue. 

63 


64  THE   TISSUES. 

6.  Fat  tissue. 

r  (a)   Hyaline. 

7.  Cartilage.  X  (b)   Elastic. 

L  (c)   Fibrous. 

8.  Bone  tissue. 

9.  Neuroglia. 

I.  Fibrillar  Connective  Tissue. 

Fibrillar  connective  tissue,  also  known  as  white  fibrous  tissue  or 
connective  tissue  proper,  consists  of  cells  and  fibres  lying  in  a  base- 
ment or  ground  substance.  The  elements  of  fibrillar  tissue  may  be 
classified  as  follows : 

f  (a)   Fixed  cells. 
Ce]ls  J  (b)  Wandering  cells. 

(c)  Plasma  cells. 

(d)  Mast  cells. 


white  or  fibrillated, 


(fl\  Fibres 
2.  Intercellular  substance.  -J  I  yellow  or  elastic. 


(b)  Ground  or  basement  substance. 
I.  Connective-Tissue  Cells. — (a)  Fixed  connective-tissue  cells 
are  flat,  irregularly  stellate  cells  with  many  branches  (Fig.  25).  The 
nucleus  lies  in  the  thickest  part  of  the  cell.  The  cytoplasm  is  usu- 
ally clear  or  slightly  granular.  Each  cell  lies  in  a  cell  space  or 
lacuna.  From  the  cell  spaces  minute  channels  (canaliculi)  extend 
in  all  directions  to  unite  with  canaliculi  from  adjoining  spaces  (Fig. 
24).  Delicate  cell  processes  extend  into  the  canaliculi  and  there 
anastomose  with  processes  from  other  cells  (Fig.  25).  Owing  to  the 
extreme  sensitiveness  of  the  protoplasm  of  the  connective-tissue  cell 
to  most  fixatives,  its  usual  appearance  is  that  of  a  minute  amount  of 
cytoplasm  shrunken  down  around  a  nucleus. 

(b)  Wandering  cells  are  not  properly  a  part  of  the  connective- 
tissue  structure.  They  are  amoeboid  white  blood  cells  (see  page 
86)  which  have  passed  out  from  the  vessels  into  the  tissues. 

(c)  Plasma  Cells. — These  cells  occur  mainly  near  the  smaller 
blood-vessels.  Their  protoplasm  is  finely  granular  and  stains  with 
basic  aniline  dyes.  They  frequently  contain  vacuoles.  Small  plasma 
cells  are  about  the  size  of  leucocytes,  which  they  closely  resemble. 
Large  plasma  cells  are  larger  than  leucocytes  and  richer  in  proto- 
plasm. 


THE   CONNECTIVE    TISSUES. 


65 


(d)  Mast  cells  are  spherical  or  irregular-shaped  cells,  found  like 
the  preceding  in  the  neighborhood  of  the  blood-vessels.  Their 
protoplasm  contains  coarse  granules  which  stain  intensely  with  basic 
aniline  dyes.  They  are  believed  by  some  investigators  to  be  connected 
with  the  formation  of  fat ;  by  others  to  represent  a  stage  in  the  devel- 
opment of  the  fixed  connective-tissue  cell. 

Connective-tissue  cells  may  be  pigmented  (Fig.  26).  In  such 
cells  the  cytoplasm  is  more  or  less  filled  with  brown  or  black  pig- 


4      P 


b 


,  ■.. 


J 


FIG.  23. — Fibrillar  Connective  Tissue  (Areolar  Type)  from  Subcutaneous  Tissue  of  Rabbit 
(technic  2,  p.  70).  X  500.  a,  Fixed  connective-tissue  cell;  b,  fibriilated  fibres  ;  c,  elastic 
fibre  with  curled  broken  end  ;  d,  elastic  fibres  showing  Y-shaped  branching. 


ment  granules.  In  man  pigmented  connective  tissue-cells  occur  in 
the  skin,  choroid  and  iris. 

2.  The  Intercellular  Substance.— (V?)  Fibres.  White  or  fibrii- 
lated fibres  are  bundles  of  extremely  fine  fibrillar  (0.5  ,".  in  diam- 
eter) (Fig.  23).  The  fibrillar  lie  parallel  to  one  another  and  are 
united  by  a  small  amount  of  cement  substance.  The  fibrillar  do  not 
branch.  The  fibre  bundles,  on  the  other  hand,  branch  dichotomously 
and  anastomose.      White  fibres,  on  boiling,  yield  gelatin. 

Yellow  or  clastic  fibres  are  apparently  homogeneous,  highly  re- 
fractive fibres,  varying  in  diameter  from  1  to  10  p.  (Fig.  23V  They 
branch  and  anastomose,  forming  networks.  The  smaller  fibres  are 
5 


66  THE    TISSUES. 

round  on  cross  section,  the  larger  flattened  or  hexagonal  (Figs.  28 
and  29).  Their  elasticity  is  easily  demonstrated  in  teased  specimens 
by  curling  of  the  broken  ends  of  the  fibres  (Fig.  23).     On  boiling 


;. 


■  /inn 

FIG.  24.— Section  of  Human  Cornea  Cut   Tangential  to  Surface,   X   350  (technic  9,  p.  71),  to 
show  Connective-tissue  Cell  Spaces  (Lacunas)  and  Anastomosing;  Canaliculi. 

they  yield  elastin.      While  apparently  homogeneous  when   subjected 
to  the  usual  technic,  Mall  describes  an  elastic  fibre  as  composed  of  a 


|</ 

■~^®£§:$%Z^ 

■  /  /    * 

!      /  )    /       /        /      ■ 

y.,/,.\  '■■■' 

....  .  £ 

J& 


X.  «' 


Jb-n 


'•■/' 5/ 


FiG.  25.— Section  of  Human  Cornea  Cut  Tangential  to  Surface,   X  350  (technic  8,  p.  71),  to 
Show  Connective-tissue  Cells  with  Anastomosing  Processes. 

thin  sheath  or  membrane,  enclosing  a  granular  substance,  elastin. 
The  latter  stains  intensely  with  magenta,  the  sheath  remaining  un- 
stained. 


THE   CONNECTIVE    TISSUES. 


67 


1  ':'■'  ~^Wi 


Fig.  26. — Pigmented  Connective-tissue  Cells  from  Choroid 
Coat  of  Human  Eye.   X  350.    (Technic  7,  p.  71.) 


(&)  Basement  or  ground  substance  occurs  in  extremely  minute 
amounts  between  the  individual  fibrillar  of  the  white  fibres,  where  it 
acts  as  a  cement  substance.  The  same  material  also  forms  the  base- 
ment or  ground  substance  t  #_. 
in  which  the  connective- 
tissue  cells  and  fibres  lie 
(Fig.  24).  Difficulty  in 
seeing  this  ground  sub- 
stance is  due  to  its  trans- 
parency.  It  may  be 
demonstrated  by  staining 
with  silver  nitrate  (see 
technic  9,  p.  71). 

Much  variation  exists 
in  regard  to  the  proportions  of  the  different  elements.  This  gives 
rise  to  variations  in  the  physical  characteristics  of  the  tissue.  When 
fibres  predominate  and  cells  are  few,  the  tissue  is  dense  and  hard 
and  is  known  as  dense  fibrous  tissue.  The  terms  fine  connective 
tissue  and  coarse  connective  tissue  designate  the  character  of  the 
fibres.  When  many  cells  are  present,  the  tissue  is  softer  and  is 
known  as  cellular  connective  tissue. 

According  to  the  arrangement  of  the  white  fibres,  fibrous  connec- 
tive tissue   is    subdivided   as 

%  "";%_  ^K^^:^sJ     \fv  -     -       ^      "5  W%      follows  : 

--^h^/^.j ■■;■-;"      .    -v     :\;^;-     ;:  (1)  Areolar    or    Loose 

:--j^  -:^--^\  -S--  ':'"    —  £"3^  Connective    Tissue. — In 

@js  ~  ----"--". L      ^r-?'1'7^    ■•;_-.  .--___;„;■  ^--7 j  this  the   fibres   are   irregular, 

^^S^^-l&f^i^^al^^^-^r1^-^  ^Jigj  running  in  all  directions  and 

-  ^^ %-- -/    T.^ -"""-  ^~^ -.-_  ■_-    ~=::V'^  interlacing,    leaving   between 

l S ~\y'  :  _  il  =  _v-_c ......  _._.,_. ,.     .    :-  -~  £:  "V  ^-"1-  them  meshes   or  arcohc  {  Fig. 

(2)  Formed  Connective 
Tissue. — In  this  the  fibres  all 
run  in  approximately  the  same 
direction,  and  are  united  by 
a  small  amount  of  ground  substance  (Fig.  27).  There  are  but  few 
cells  and  these  are  flattened  out  by  pressure  and  lie  between  the 
fibres,  their  long  axes  corresponding  to  the  direction  of  the  fibres. 
This  arrangement   of  tissue   elements  forms   a    firm,  dense    tissue, 


FIG.  27.— Longitudinal  Section  of  Tendon  from 
Frog's  Gastrocnemius.  X  250.  The  nuclei  of 
the  flattened  cells  are  seen  lying  in  rows  be- 
tween the  connective-tissue  fibres. 


68  THE   TISSUES. 

such  as  is  found  in  tendons  and  ligaments.  Formed  connective 
tissue  also  occurs  as  anastomosing  networks  of  fibres,  as,  e.g.,  in 
the  omentum  (page  60),  and  as  thin  membranes,  such  as  the  inter- 
muscular septa  and  fascia  in  general. 

Regarding  the  development  of  the  connective-tissue  fibrils,  there 
are  two  theories:  (1)  According  to  one,  they  are  developed  directly 
from  the  protoplasm  of  the  connective-tissue  cells.  The  cells  in- 
crease in  length,  and  fine  granules  appear,  which  arrange  themselves 
in  rows  in  the  cytoplasm ;  these  granules  unite  to  form  fibrils. 
Such  cells  are  known  as  fibroblasts,  and  their  fibrils  are  the  forerun- 
ners of  the  intercellular  fibrils  of  connective  tissue.  A  modification 
of  this  theory  derives  the  fibrils  from  the  peripheral  portion  of  the 
cell — the  exoplasm.  (2)  According  to  the  other  theory  the  fibrils  are 
developed  from  the  matrix,  minute  granules  first  becoming  arranged 
in  rows  and  later  uniting  to  form  fibrils. 

Regarded  as  opposing  theories,  there  is  in  reality  but  little  an- 
tagonism between  them.  There  is  no  doubt  as  to  the  intercellular 
matrix  being  a  product  of  the  cell.  Whichever  theory,  therefore,  is 
accepted,  the  entire  intercellular  substance,  fibres  and  ground  sub- 
stance are  ultimate  derivatives*  of  the  cell.  Recent  studies,  espe- 
cially those  of  Mall,  are  confirmatory  of  the  second  of  the  theories 
given  above.  He  maintains  that  the  connective-tissue  fibrils,  both 
white  and  elastic,  are  derivatives  of  an  active  intercellular  matrix, 
which  latter  is  a  direct  product  of  the  cell. 

Two  similar  theories  exist  as  to  the  development  of  elastic  fibres, 
a  cellular  theory  and  an  extracellular  theory.  According  to  some 
advocates  of  the  cellular  theory,  the  elastic  fibres  are  derived  from 
the  exoplasm ;  according  to  others,  from  the  cytoplasm  immediately 
surrounding  the  nucleus.  Recent  researches  favor  the  extracellular 
theory.  Mall  describes  extremely  minute  fibrils  in  the  ground  sub- 
stance, which  later  develop  into  elastic  fibres. 

2.  Elastic   Tissue. 

lilastic  fibres  occurring  in  fibrous  connective  tissue  have  been 
described.  When  the  elastic  fibres  are  greater  in  amount  than  the 
white  fibres,  the  tissue  is  known  as  elastic  tissue.  Almost  pure 
elastic  tissue  is  found  in  the  ligamentum  nucha?  of  quadrupeds. 
Here  the  fibres  are  coarse  and  held  together  by  a  small  amount  of 
cement  substance.  A  few  white  fibres  and  connective-tissue  cells 
are  also  present  (Figs.  28  and  29). 

Elastic  tissue  may  be  arranged  as  thin  membranes,  as,  e.g., 
in   the  walls   of   blood-vessels.     These    membranes  are  usually    de- 


THE   CONNECTIVE    TISSUES. 


69 


scribed  as   composed   of    a    dense  mass  of   flat,    ribbon-like  elastic 
fibres,  which  interlace  in  such  a  manner  as  to  leave  openings  in  the 


Fig.  28. — Coarse  Elastic  Fibres  from  Ligamentum  Nuchas.     X  500.     Teased  specimen.     (Tech- 

nic  10,  p.  71.) 

membrane.  Hence  the  term  "fenestrated  membrane."  They  have 
been  recently  described  as  consisting  of  a  central  layer  composed  of 
elastin,  staining  with  magenta,  and  on  either  side  a  thin,  transparent 


,-£ 


I 


Fig.  29.  — Cross  Section  of  Coarse  Elastic  Fibres  from  Ligamentum  Nuchas.  X  500.  (Tech- 
nic  10,  p.  71).  a,  Elastic  fibres  ;  b,  white  fibrous  tissue  and  cement  substance.  The  nu- 
clei are  the  nuclei  of  fixed  connective-tissue  cells. 

sheath  unstained  by  magenta.  This  is  seen  to  correspond  to  Mall's 
description  of  the  structure  of  the  elastic  fibre.  Only  the  middle  of 
these  layers  is  fenestrated. 


;o  THE   TISSUES. 


TECHNIC. 

i.  Areolar  Tissue,  to  show  White  and  Elastic  Fibres.— Remove  a  bit  of  the 
subcutaneous  tissue,  as  free  from  fat  as  possible,  from  a  recently  killed  animal. 
Place  it  upon  a  mounting  slide  and  with  teasing  needles  quickly  spread  it  out  in 
a  thin  layer.  During  this  manipulation  the  specimen  should  be  kept  moist  by 
breathing  on  it.  Put  a  drop  of  sodium  chlorid  solution  upon  the  specimen  and 
cover. 

As  the  specimen  is  unstained,  a  small  diaphragm  should  be  used  for  the  micro- 
scopic examination. 

The  white  fibres  are  straight  or  wavy,  are  crossed  in  all  directions,  and  are 
longitudinally  striated.  The  elastic  fibres  have  been  stretched  and  show  as  sharp 
lines  with  curled  ends  where  the  fibres  are  broken. 

Place  a  drop  of  hydric  acetate,  i-per-cent  aqueous  solution,  at  one  side  of  the 
cover  and  a  bit  of  filter  paper  at  the  other  side.  The  filter  paper  absorbs  the  salt 
solution,  which  is  replaced  by  the  hydric  acetate.  The  latter  causes  the  white 
fibres  to  swell  and  become  indistinct  while  the  elastic  fibres  show  more  plainly. 

2.  Areolar  Tissue,  to  show  Cells  and  Elastic  Fibres. — Prepare  second  speci- 
men of  areolar  tissue  in  the  same  manner  as  the  preceding.  Instead  of  mounting 
in  salt  solution,  allow  it  to  become  perfectly  dry,  then  stain  in  the  following  solu- 
tion : 

Gentian  violet  saturated  aqueous  solution 40  c.c. 

Water 60  c.c. 

Wash  thoroughly,  dry,  and  mount  in  balsam. 

The  nuclei  of  the  fixed  connective-tissue  cells  are  stained  violet.  Their  deli- 
cate cell  bodies  show  as  an  irregular  haze  around  the  nuclei.  Both  nuclei  and  cell 
bodies  appear  cut  in  all  directions  by  the  stretched  elastic  fibres.  Wandering  cells 
(leucocytes)  may  usually  be  seen.  Plasma  cells  are  frequently  not  demonstrable, 
and  mast  cells  are  only  occasionally  present.  The  elastic  fibres  are  stained  violet. 
The  white  fibres  are  almost  unstained. 

3.  Formed  Connective  Tissue. — Fibrous  tissue  arranged  in  the  form  of  a  net- 
work may  be  seen  in  the  specimen  of  omentum  (technic  7,  p.  62). 

4.  Densely  formed  connective  tissue  may  be  studied  in  tendon.  Cut  through 
the  skin  of  the  tail  of  a  recently  killed  mouse  about  half  an  inch  from  the  tip  and 
break  the  tail  at  this  point.  By  pulling  on  the  end  of  the  tail  this  portion  may  now 
be  separated  from  the  rest  of  the  tail,  carrying  with  it  long  delicate  tendon  fibrils, 
which  have  been  pulled  out  of  their  sheaths.  This  should  be  immediately  ex- 
amined in  salt  solution,  using  the  high  power  and  a  small  diaphragm.  The  fibrils 
are  seen  arranged  in  parallel  bundles. 

5.  Place  a  drop  of  hydric  acetate  (2-per-cent  aqueous  solution)  at  one  side  of 
the  cover-glass,  absorbing  the  salt  solution  from  the  opposite  side  by  means  of 
filter  paper.  The  fibres  swell  and  become  almost  invisible,  while  rows  of  connec- 
tive-tissue cells  (tendon  cells)  can  now  be  seen.  The  cells  may  be  stained  by  allow- 
ing a  drop  of  heematoxylin  or  of  carmine  solution  to  run  under  the  cover.  After 
the  cells  are  sufficiently  stained,  the  excess  of  stain  is  removed  by  washing  and  the 
specimen  mounted  in  glycerin. 

(>.  Fix  a  small  piece  of  any  good-sized  tendon  in  formalin-Muller's  fluid  (page 
5).     After  a  week,  harden   in   alcohol,  embed  in   celloidin,  and  make  longitudinal 


THE  CONNECTIVE   TISSUES.  71 

and  transverse  sections.  Stain  strongly  with  hematoxylin,  followed  by  picro-acid 
fuchsin  (page  16).     Mount  in  balsam. 

7.  Pigmented  connective-tissue  cells  are  most  conveniently  obtained  from  the 
choroid  coat  of  the  eye.  Fix  an  eye  in  formalin-Midler's  fluid  (see  page  5).  cut 
in  half,  remove  choroid  and  retina  and  pick  off  the  dark  shreds  which  cling  to  the 
outer  surface  of  the  choroid  and  inner  surface  of  the  sclera.  These  may  be  trans- 
ferred directly  to  glycerin,  in  which  they  are  mounted,  or  the  bits  of  tissue  may  be 
first  stained  with  hematoxylin  (page  13).  In  addition  to  the  pigmented  cells 
should  be  noted  the  ordinary  fixed  connective-tissue  cells  which  lie  among  them. 
Only  the  nuclei  of  these  cells  can  be  seen. 

8..  Connective-Tissue  Cells  to  show  Anastomosing  Processes. — Stain  a  cornea 
with  gold  chlorid  (see  page  23).  Sections  are  made  tangential  to  the  convex  sur- 
face and  are  mounted  in  glycerin. 

9.  Connective-tissue  cell  spaces  (lacunae)  and  their  anastomosing  canaliculi 
may  be  demonstrated  by  staining  a  cornea  with  silver  nitrate  (see  page  23).  The 
silver  stains  the  ground  substance  of  the  cornea,  leaving  the  lacunae  and  canaliculi 
unstained.  The  relation  which  this  picture  bears  to  the  preceding  should  be  borne 
in  mind  (see  Figs.  24  and  25). 

10.  Coarse  elastic  fibres  may  be  obtained  from  the  ligamentum  nuchas,  which 
consists  almost  wholly  of  elastic  tissue.  A  piece  of  the  ligament  is  fixed  in  satu- 
rated aqueous  solution  of  picric  acid  and  hardened  in  alcohol.  A  bit  of  this  tissue 
is  teased  apart  on  a  glass  slide  in  a  drop  of  pure  glycerin,  in  which  it  is  also 
mounted.  Before  putting  into  glycerin,  the  specimen  may  be  stained  with  picro- 
acid-fuchsin.  This  intensifies  the  yellow  of  the  elastic  fibres  and  brings  out  in  red 
the  fibrillar  connective  tissue.  Pieces  of  the  ligament  fixed  and  hardened  in  the 
same  manner  may  be  embedded  in  celloidin  and  cut  into  longitudinal  and  trans- 
verse sections.  These  stained  with  picro-acid-fuchsin  show  well  the  relation  of 
the  coarse  elastic  fibres  (yellow)  to  the  more  delicate  fibrous  tissue  (red). 


3.  Embryonal  and  Mucous  Tissue. 

Embryonal  and  mucous  tissue  represent  an  early  differentiation 
from  the  general  type  of  embryonic  connective  tissue.  They  consist 
according  to  their  age  of  oval,  fusiform,  or  irregular  branching  and 
anastomosing  cells,  lying  in  a  matrix,  which  is  just  beginning  to 
show  evidences  of  a  fibrillar  structure.  By  some  histologists  the 
term  "embryonic"  connective  tissue  is  limited  to  the  stage  of  fusi- 
form cells  with  slightly  fibrillar  matrix  (Fig.  30),  the  term  "  mucous  " 
tissue  being  applied  to  an  embryonic  form  of  connective  tissue  in 
which  irregular  branching  and  anastomosing  cells  lie  in  a  slightly 
fibrillated  matrix  which  gives  the  chemical  reaction  for  mucin 
(Fig-  3i)- 

Much  variation  exists  as  to  the  shape  and  size  of  the  cells  in  em- 
bryonal and  mucous  tissue.  This  is  due  to  the  fact  that  these  cells 
represent  transition  stages  in  the  development  of  the  adult  connec- 


7* 


THE    TISSUES. 


tive-tissue  cell.     Thus  in  embryonic  connective  tissue,  while  most 
of  the  cells  are  fusiform,  one  finds  spherical  and  oval  cells  and  some 


Fig.  30.— Embryonal  Connective  Tissue  from  Axilla  of  Five-inch  Foetal  Pig.  X  600.  (Technic 
1,  p.  73.)  Various  shaped  connective-tissue  cells  are  seen  lying  in  a  slightly  fibrillated 
matrix. 

few  cells  which  are  triangular  or  stellate.  The  same  holds  true  of 
mucous  tissue,  where,  while  most  of  the  cells  are  of  the  triangular 
or  stellate  variety,  round,  oval  and  fusiform  cells  are  also  present. 


m  1  • 


Fig.  31.— Mucous  Connective  Tissue  from  Umbilical  Cord  of  Eight-inch  Foetal  Pig.    X  600. 

(Technic  2,  p.  73.) 


THE   CONNECTIVE    TISSUES.  73 


TECHNIC. 

r.  Embryonal  Tissue.— Bits  of  the  subcutaneous  tissue  from  the  axilla  or  groin 
of  a  five-inch  foetal  pig  are  fixed  in  Zenker's  fluid  (technic  6,  p.  9),  hardened  in 
alcohol  and  stained  for  twelve  hours  in  alum-carmine  (technic  Z>,  p.  15;.  They 
are  then  transferred  to  eosin-glycerin,  in  which  they  are  teased  and  mounted. 
Note  the  intercellular  substance,  that  it  is  composed  of  delicate  single  fibrils  inter- 
lacing in  all  directions  with  no  arrangement  into  bundles,  as  in  adult  tissue,  and 
that  there  is  as  yet  no  differentiation  into  two  kinds  of  fibres. 

2.  Mucous  Tissue. — The  umbilical  cord  of  a  three  to  four  months  human  foe- 
tus, or  of  a  nine-inch  foetal  pig  is  fixed  in  formalin-Midler's  fluid  (page  5).  hard- 
ened in  alcohol,  and  transverse  sections  stained  with  haematoxylin-eosin  (technic  1, 
p.  16)  and  mounted  in  eosin-glycerin.  Note  the  central  blood-vessels  with  their 
thick  walls  and  the  surface  epithelium.  The  mucous  tissue  is  best  studied  near  the 
surface  just  beneath  the  epithelium. 


4.  Reticular  Tissue. 

Reticular  connective  tissue  is  a  form  of  fibrillar  connective  tissue. 
It  consists  of  small  bundles  of  extremely  delicate  white  fibrillae. 
These  interlace  in  all  directions  and  form  a  network  enclosing  spaces 
of  various  sizes  and  shapes  (Fig.  32).      The  cells  are  flat  and  wrap 


FIG.  32.— Reticular  Connective  Tissue  from  Human  Lymph  Node.  X  600.  (Technic,  p.  7^.) 
The  nuclei  belong  to  flat  connective-tissue  cells  which  lie  upon  the  fibres  of  the  reticulum, 
their  cell  bodies  being-  invisible. 

themselves  around  the  bundles  of  fibrils.  This  led  to  the  belief  that 
reticular  connective  tissue  was  composed  wholly  of  anastomosing 
cells. '  Later,  when  the  underlying  fibrillar  basis  was  understood,  the 
overlying  cells  were  referred  to  as  "  epithelioid  "  cells,  the  designation 
being  based  upon  morphological  characteristics.      With  the  recogni- 

1  In  some  lower  animals  and   in  the  embryos  of  some   higher  animals,  such 
wholly  cellular  reticular  tissues  are  found. 


74 


THE    TISSUES. 


tion  of  the  impossibility  of  differentiating  on  a  morphological  basis 
between  certain  forms  of  epithelial  and  of  connective-tissue  cells, 


<^ 


>"^m  i  ® 


,5(8)  *    -*at 


-,^-;-. 


m  'v"'"  ® 


#  •iT\  % 


t" 


© 


i© 


Fig.  33. — Diffuse  Lymphatic  Tissue  from  Human  Lymph  Node.     X  600.     (Technic,  p.  75.) 

these  cells  were  classified  where  their  histogenesis  properly  places 
them,  as  connective-tissue  cells. 

Reticular  connective  tissue  differs  in  chemical  composition  from 


FIG.  34.— Circumscribed  Lymphatic  Tissue  from  Human  Lymph  Node.     X  450.     (Technic, 

P.    75) 

both    fibrous  and   elastic   tissue.      Reticular  connective  tissue  forms 
the  framework  of  adenoid  tissue  and  of  bone  marrow.     Fibrils  giving 


THE   CONNECTIVE   TISSUES.  75 

the  chemical  reaction  of  reticular  tissue  are  associated  with  the 
fibrous  and  elastic-tissue  framework  of  the  lung,  liver,  kidney  and 
other  organs. 

5.  Lymphatic  Tissue. 

Lymphatic  tissue  consists  of  reticular  connective  tissue  and  lym- 
phoid cells,  the  latter  filling  the  meshes  of  the  reticulum.  Lym- 
phoid cells  are  small  spherical  cells.  Each  cell  has  a  single  nucleus 
which  almost  fills  the  cell. 

Lymphatic  tissue  may  be  diffuse  or  circumscribed.  In  diffuse 
lymphatic  tissue  (Fig.  33)  the  cells  are  not  closely  packed  and  there 
is  no  distinct  demarcation  between  the  lymphatic  and  the  surround- 
ing tissues.  An  example  of  diffuse  lymphatic  tissue  is  seen  in  the 
stroma  of  the  mucous  membrane  of  the  gastro-intestinal  canal.  In 
circumscribed  lymphatic  tissue  (Fig.  34)  the  cells  are  very  closely 
packed,  often  completely  obscuring  the  reticulum.  There  is  also  a 
quite  distinct  demarcation  between  the  lymphatic  and  the  surround- 
ing tissues.  Such  a  circumscribed  mass  of  lymphatic  tissue  is  known 
as  a  lymph  nodule. 

TECHNIC. 

Fix  a  lymph  node  in  formalin-Miiller's  fluid  (technic  5,  p.  5).  and  stain  very 
thin  sections  with  hematoxylin  and  picro-acid-fuchsin  (technic  3,  p.  16).  In  the 
lymph  sinuses  of  the  medulla  the  reticulum  can  usually  be  plainly  seen.  This 
specimen  serves  also  for  the  demonstration  of  diffuse  and  compact  lymphatic  tis- 
sue, the  former  in  the  lymph  sinuses  of  the  medulla,  the  latter  in  the  nodules  of  the 
cortex  and  in  the  medullary  cords. 

6.  Fat  Tissue. 

Adipose  tissue  or  fat  tissue  is  a  form  of  connective  tissue  in  which 
most  of  the  cells  have  become  changed  into  fat  cells.  Fat  tissue  is 
peculiar  among  the  connective  tissues  in  that  the  cells  and  not  the 
intercellular  substance  make  up  the  bulk  of  and  determine  the  char- 
acter of  the  tissue.  The  adult  fat  cell  is  surrounded  by  a  distinct 
cell  membrane,  and  almost  the  entire  cell  is  occupied  by  a  single 
spherical  droplet  of  fat  (Figs.  36  and  37).  The  nucleus,  flattened 
and  surrounded  by  a  small  amount  of  cytoplasm,  is  usually  found 
pressed  against  the  cell  wall  (Fig.  37).  This  appearance  of  a  dis- 
tinct cell  membrane  enclosing  the  spherical  fat  droplet,  with  the 
nucleus  and  cytoplasm  pressed  into  a  crescent-shaped  mass  at  one 


76 


THE    TISSUES. 


side,  has  given  rise  to  the  term  "  signet-ring  cell."      Fat  cells  which 
occur  singly,  or  in  small  groups,  or  in  the  developing  fat  of  young 


Fig.  35.— Fat  Tissue  from  Human  Subcutaneous  Tissue  (Child)  to  show  Lobulation.     X  25. 

(Technic  1,  p.  79.) 

b 


Young  Fat  from  Human  Subcutaneous  Tissue  (Child).  X  175.  (Technic  r,  p.  79.) 
a.  Interlobular  connective  tissue  ;  /■>,  fixed  connective-tissue  cell  ;  c,  fat  cells;  d,  artery  ; 
e,  nucleus  of  fat  cell  and  remains  of  cytoplasm  ("signet  ring'"). 


THE   CONNECTIVE   TISSUES.  77 

animals,  are  spherical  (Fig.  36).  In  large  masses  of  adult  fat,  the 
closely  packed  cells  are  subjected  to  pressure  and  are  polyhedral 
(Fig.  37).  Adult  fat  cells  are  usually  arranged  in  groups  or  lobules, 
each  lobule  being  separated  from  its  neighbors  by  fibrillar  connective 
tissue  (Fig.  35).  Adipose  tissue  is  usually  associated  with  loose 
fibrous  tissue. 

The  appearance  which  adult  fat  presents  can  be  understood  only 
by  reference  to  its  histogenesis.  Fat  cells  are  developed  directly 
from  embryonic  connective-tissue  cells.  In  the  human  embryo  they 
are  first  distinguishable  as  fat  cells  about  the  thirteenth  week.      The 


d  c 

FIG.  37.— Adult  Fat  Tissue  from  Human  Subcutaneous  Tissue.  X  175-  (Technic  1,  p.  79.) 
a,  Fat  cells  ;  b,  interlobular  connective  tissue  ;  c,  nucleus  of  fat  cell  and  remains  of  cyto- 
plasm (  "  signet  ring  ")  ;  d,  artery. 

connective-tissue  cells  which  are  to  become  fat  cells  gather  in 
groups  in  the  meshes  of  the  capillary  network  which  marks  the  end- 
ing of  a  small  artery.  Each  group  is  destined  to  become  an  adult 
fat  lobule  (Fig.  38). 

Fat  first  appears  as  minute  droplets  in  the  cytoplasm  of  the  em- 
bryonic connective-tissue  cell  (Fig.  39).  These  small  droplets  in- 
crease in  number  and  finally  coalesce  to  form  a  single  larger  droplet. 
This  increases  in  size  and  ultimately  almost  wholly  replaces  the  cyto- 
plasm. In  this  way  the  nucleus  and  remaining  cytoplasm  are  pressed 
to  one  side  and  come  to  occupy  the  inconspicuous  position  which 
they  have  in  adult  fat. 


78 


THE    TISSUES. 


The  blood  supply  of  fat  is  rich  and  the  adult  lobule  maintains 
its  embryonic  vascular  relations,  in  that  the  vascular  supply  of  each 
lobule  is  complete  and  independent.      One  artery  runs  to  each  lobule, 


Fig.  38. — Developing  Fat  Tissue  from  Subcutaneous  Tissue  of  Five-inch  Foetal  Pig.  X  75. 
(Technic  2,  p.  79.)  a,  Arteriole  breaking  up  into  capillary  network  ;  b,  embryonal  con- 
nective tissue  ;  c,  embryonal  fat  lobules  developing  around  blood-vessels. 


Fig.  39 —Developing  Fat  Tissue  from  Subcutaneous  Tissue  of  Five-inch  Fcetal  Pig. 
(Technic  2,  p.  79. j    a,  Arteriole  breaking  up  into  capillary  network;  6,  embryor. 


X  35°- 
yonal  con- 
nective tissue,  embryonal  cells  from  which  fat  cells  are  developing;  c,  capillaries ;  fat 
droplets  stained  black.  Cells  are  seen  in  all  stages  of  transition  from  embryonal  connec- 
tive-tissue cells  containing  a  few  fat  droplets  to  cells  in  which  the  cytoplasm  is  almost 
completely  replaced  by  fat. 


THE   CONNECTIVE    TISSUES.  79 

where  it  breaks  up  into  an  intralobular  capillary  network,  which  in 
turn  gives  rise  to  the  intralobular  veins,  usually  two  in  number. 

Fat  is  thus  seen  to  be  a  connective  tissue  in  which  some  of  the 
cells  have  undergone  specialization.  There  still  remain,  however, 
embryonal  connective-tissue  cells  which  are  not  destined  to  become 
fat  cells,  but  which  develop  into  cells  and  fibres  of  ordinary  fibrous  con- 
nective tissue.  A  few  of  these  remain  among  the  fat  cells  to  become 
the  delicate  intralobular  connective  tissue  seen  in  adult  fat.  The 
majority  are,  however,  pushed  to  one  side  by  the  developing  lobules, 
where  they  form  the  interlobular  septa. 

TECHNIC. 

i.  Fat  Tissue. — Human  subcutaneous  fat  as  fresh  as  possible  is  fixed  in  forma- 
lin-Miiller's  fluid  (technic  5,  p.  5),  hardened  in  alcohol  and  embedded  in  celloidin. 
Sections  are  stained  with  haematoxylin  and  picro-acid-fuchsin  (technic  3,  p.  16). 
The  alcohol  and  ether  of  the  celloidin  remove  the  fat  from  the  fat  cells,  leaving 
only  the  cell  membranes.  The  fat  gives  the  celloidin  a  milky  appearance.  Such 
celloidin  does  not  cut  well.  The  celloidin  should,  therefore,  be  changed  until  it 
ceases  to  turn  white.  The  sections  are  cleared  in  oil  of  origanum  or  carbol  xylol, 
and  mounted  in  balsam.  The  fibrillar  tissue  is  stained  red  by  the  fuchsin,  and  the 
protoplasm  of  the  fat  cell  yellow  by  the  picric  acid. 

2.  Developing  Fat  Tissue. — Remove  bits  of  tissue  from  the  axilla  or  groin  of 
a  five-inch  foetal  pig,  or  other  foetus  of  about  the  same  development.  Fix  twenty- 
four  hours  in  a  i-per-cent  aqueous  solution  of  osmic  acid  (technic  6,  p.  24),  wash 
thoroughly  and  mount  in  glycerin.  A  part  of  the  tissue  mounted  should  be  thor- 
oughly teased,  the  rest  gently  pulled  apart.  The  teased  portion  will  show  the  fat 
cells  in  various  stages  of  development.  The  unteased  part  will  usually  show 
brownish  blood-vessels  and  the  grouping  of  fat  cells  around  them,  to  form  embry- 
onic fat  lobules.  Note  the  developing  connective  tissue  between  the  groups  of  fat 
cells.  It  is  from  this  that  the  areolar  tissue,  which  envelops  and  separates  the 
lobules  of  adult  fat,  is  developed. 


7.  Cartilage. 

Cartilage  is  a  form  of  connective  tissue  in  which  the  ground  sub- 
stance is  firm  and  dense  and  determines  the  physical  character  of  the 
tissue.  Cartilage  cells  are  differentiated  connective- tissue  cells. 
While  varying  greatly  in  shape  they  are  most  frequently  spherical  or 
oval.  Each  cell  lies  in  a  cell  space  or  lacuna,  which  it  completely 
fills.  The  intercellular  substance  immediately  surrounding  a  lacuna 
is  frequently  arranged  concentrically,  forming  a  sort  of  capsule. 
Fine  canaliculi  connecting  the  lacuna?  are  present  in  some  of  the 
lower  animals  and   have  been  described  in  human  cartilage.     They 


8o 


THE    TISSUES. 


can  be   demonstrated,  however,  in   human   cartilage,  only  by  special 
methods,  and  probably  represent  artefacts. 

Cartilage  contains   no   blood-vessels,  and   in   human  cartilage  no 
lymph  channels  have  been  positively  demonstrated. 


4?3  .-•■ 


m& 


■■■■ 


* 


mi 


<m  m 


m 


(SHIP 


Fig.  40.— Hyaline  Cartilage  from  Head  of  Frog's  Femur.     X  350.     (Technic  1,  p.  S2.)    Groups 
of  cartilage  cells  in  apparently  homogeneous  matrix. 


Cartilage  is  subdivided  according  to  the  character  of  its  intercel- 
lular substance  into  three  varieties  :  (1)  Hyaline,  (2)  elastic,  (3)  fibrous. 
1.  Hyaline  Cartilage  (Fig.  40). — The  cells  occur  singly  or  in 


groups  of  two  or  multiples  of  two. 


{'- 


1    i 


FIG.  41.— Elastic  Cartilage  from  Dog's  Ear. 
[o.    c'l'echnic  2,  p.  82.)    Groups  of  car- 
tilage cells  in  fibro-elastic  matrix. 


An  entire  group  of  cells  frequent- 
ly lies  in  one  lucuna  surrounded 
by  a  single  capsule.  Such  a 
group  of  cells  has  developed 
within  its  capsule  from  a  single 
parent  cell.  In  other  cases  del- 
icate hyaline  partitions  separate 
the  cells  of  a  group.  The  cells 
are  spherical  or  oval,  with  flatten- 
ing of  adjacent  sides.  The  nu- 
cleus is  centrally  placed,  and 
has  a  distinct  intranuclear  net- 
work and  membrane.  The  cyto- 
plasm is  finely  granular,  and  may 
contain  droplets  of  fat,  of  glyco- 


THE   CONNECTIVE    TISSUES.  8 1 

gen,  or  of  both.  Toward  the  perichondrium  the  arrangement  of  the 
cells  in  groups  is  less  distinct.  Here  the  cells  are  fusiform  and 
parallel  to  the  surface. 

The  intercellular  matrix,  when  subjected  to  the  usual  technic, 
appears  homogeneous.  By  the  use  of  special  methods,  such,  e.g.,  as 
artificial  digestion,  this  apparently  structureless  matrix  has  been 
shown  to  be  made  up  of  bundles  of  fibres,  quite  similar  to  those 
found  in  fibrous  connective  tissue. 

Hyaline  cartilage  forms  the  articular  cartilages  of  joints,  the  costal 
cartilages,  and  the  cartilages  of  the  nose,  trachea,  and  bronchi.  In 
the  embryo  a  young  type  of  hyaline  cartilage,  known  as  embryonal 
cartilage,  forms  the  matrix  in  which  most  of  the  bones  are  developed. 

2.  Elastic  cartilage  (Fig.  41)  resembles  hyaline,  but  differs  from 
the  latter  in  that  its  hyaline  matrix  contains  a  large  number  of 
elastic  fibres.  These  vary  in  size,  many  being  extremely  fine. 
The  elastic  fibres  branch  and  run  in  all  directions,  forming  a  dense 
network  of  interlacing  and  anastomosing  fibres. 

Elastic  cartilage  occurs  in  the  external  ear,  the  Eustachian  tube, 
the  epiglottis,  and  in  some  of  the  laryngeal  cartilages. 

3.  Fibrous  cartilage  (Fig.  42)  is  composed  mainly  of  fibrillar 
connective  tissue.     The  fibres  may  have  a  parallel  arrangement,  or 


Fig.  42.  —  Fibrous  Cartilage  from  Dog's  Intervertebral  Disc.      X   350.     (Techuie  3,   p.  S2.) 
Groups  of  cartilage  cells  in  matrix  of  fibrillar  connective  tissue. 

may  run  in  all  directions.      Cells  are  few,  and  are   usually  arranged 
in  rows  of  from  two  to  six,  lying  in  elongated  cell  spaces  between 
the  fibre  bundles. 
6 


32  THE    TISSUES. 

Fibrous  cartilage  occurs  in  the  inferior  maxillary  and  sterno- 
clavicular articulations,  in  the  symphysis  pubis,  and  in  the  interver- 
tebral discs. 

Cartilage,  except  where  it  forms  articular  surfaces,  is  covered  by 
a  membrane,  the  perichondrium.  This  is  composed  of  fibrillar  con- 
nective tissue,  and  blends  without  distinct  demarcation  with  the 
superficial  layers  of  the  cartilage. 

Like  the  other  connective  tissues,  cartilage  develops  from  mesen- 
chyme. It  is  at  first  wholly  cellular.  Each  cell  forms  a  capsule 
around  itself,  and  by  blending  of  these  capsules  are  formed  the  first 
elements  of  the  intercellular  matrix.  This  increases  in  quantity  and 
assumes  the  structural  characteristics  of  one  of  the  forms  of  carti- 
lage. The  white  fibres  of  fibro-cartilage  and  the  yellow  fibres  of 
elastic  cartilage  develop  in  the  same  manner  as  in  fibrillar  and  elastic 
tissue. 

TECHNIC. 

(i)  Hyaline  Cartilage. — Remove  a  frog's  femur  and  immediately  immerse  the 
head  in  saturated  aqueous  solution  of  picric  acid.  Cut  sections  tangential  to  the 
rounded  head,  keeping  knife  and  bone  wet  with  the  picric-acid  solution.  As  bone 
must  be  cut,  a  special  razor  kept  for  the  purpose  should  be  used.  Cut  sections  as 
thin  as  possible.  The  first  sections  consist  wholly  of  cartilage.  As  bone  is 
reached,  the  cartilage  is  confined  to  a  ring  around  the  bone.  Mount  in  the  picric- 
acid  solution,  cementing  the  cover-glass  immediately. 

(2)  Elastic  Cartilage.— Remove  a  piece  of  cartilage  from  the  ear  and  fix  in 
formalin-Muller's  fluid  (technic  5,  p.  5).  Stain  sections  strongly  with  hematoxylin, 
followed  by  picro-acid-fuchsin  (technic  3,  p.  16).  Clear  in  carbol-xylol  and  mount 
in  balsam.  The  capsules  around  the  cartilage  cells  are  thick  and,  as  they  usually 
retain  some  hematoxylin,  can  be  readily  seen.  Note  also  the  flattened  cartilage 
cells  near  the  surface,  and  the  perichondrium. 

(3)  Fibro-cartilage. — Fix  pieces  of  an  intervertebral  disc  in  formalin-Muller's 
fluid.  Sections  are  stained  either  with  hannatoxylin-eosin  or  with  haematoxylin- 
picro-acid-fuchsin  and  mounted  in  balsam. 

8.     Bone    Tissue. 

Bone  is  a  form  of  connective  tissue  in  which  the  matrix  is  ren- 
dered hard  by  the  deposition  in  it  of  inorganic  matter,  chiefly  the 
phosphate  and  the  carbonate  of  calcium.  These  salts  are  not  merely 
deposited  in  the  matrix,  but  are  intimately  associated  and  combined 
with  its  histological  structure.  The  intimacy  of  this  association  of 
the  organic  and  inorganic  constituents  of  bone  is  shown  by  the  fact 
that,   though    the   salts   compose   two-thirds   of   bone   by  weight,   it 


THE   CONNECTIVE    TISSUES. 


33 


is    impossible    to    distinguish    them    by   the    highest   magnification. 

Furthermore,  if  either  the  lime  salts  are  dissolved   out  by  means  of 

acids  (decalcification)  or  the 

organic  matter  removed  by 

heating      (calcination),    the 

histological  structure  of  the 

bone  still  remains. 

Like  the  other  connec- 
tive tissues,  bone  consists 
morphologically  of  cells  and 
intercellular  substance. 

Bone  cells  or  bone  cor- 
puscles lie   in    distinct   cell 

Spaces  Or  laciline.       From  the    FlG-  43--Bone  Tissue   showing  Lacunae  and    Canali- 

culi.     X  700.     (Technic  1,  p.  83.) 

lacunae  pass  off  in  all  direc- 
tions minute  canals — canaliculi — which  anastomose  with  canaliculi 
of  neighboring  lacunae  (Fig.  43).  At  the  surface  of  bone  these 
canaliculi  open  into  the  periosteal  lymphatics.  A  complete  system 
of  canals  is  thus  formed,  which  traverse  the  bone  and  serve  for  the 
passage  of  nutritive  fluids.  The  bone  cells 
themselves  (Fig.  44)  are  flat,  ovoid,  nucleated 
cells,  with  numerous  fine  processes,  which 
extend  in  all  directions  into  the  canaliculi. 
In  young  developing  bones  the  processes  of 
adjacent  cells  anastomose.  In  adult  bone  the 
processes  extend  but  a  short  distance  into 
the    canaliculi,    and    probably    do    not    anas- 


FlG.    44.  — Bone    Cell    and    La-    tOniOSe 
cud"..      (After    Joseph.)     At 
a  the  cell  body  has  shrunken, 
allowing   the   outline  of  the 
lacuna  to  be  seen. 


The  basement  substance  or  matrix  has  a 
fibrous  structure,  closely  resembling  that  of 
fibrillar  connective  tissue,  and  it  is  in  this 
fibrillar  matrix  that  the  lime  salts  are  deposited.  The  fibrils  are  held 
together  by  cement  substance  into  bundles.  In  most  bone  the 
bundles  are  fine  and  arranged  in  layers  or  lamella.  Less  commonly 
the  fibre  bundles  are  coarser  and  have  an  irregular  arrangement. 


TECHNIC. 

(1)  For  the  study  of  the  minute  structure  of  bone  a  section  of  undecalcilied  or 
hard  bone  is  required.  Part  of  the  shaft  of  one  of  the  long  bones  is  soaked  for 
several  days  in  water  and  all  the  soft  parts  are  removed.     It  is  then  placed  in  equal 


84  THE   TISSUES. 

parts  alcohol  and  ether  to  remove  all  traces  of  fat  and  thoroughly  dried  (the  handle 
of  a  tooth  or  nail  brush  frequently  furnishes  good  material  and  is  already  dried). 
Thin  longitudinal  and  transverse  sections  are  now  cut  out  with  a  bone  saw.  One 
surface  is  next  ground  smooth,  first  on  a  glass  plate,  using  emery  and  water,  then 
on  a  hone.  The  specimen  is  now  fastened  polished  side  down  on  a  block  of  wood 
or  glass  by  means  of  sealing  wax.  and  the  other  side  polished  smooth  in  the  same 
manner  as  the  first,  the  bone  being  ground  as  thin  as  possible.  The  sealing  wax  is 
removed  by  soaking  in  alcohol  and  the  specimen  looked  at  with  the  low  power. 
If  not  thin  enough,  it  is  gently  rubbed  on  a  fine  hone.  It  is  then  soaked  in  equal 
parts  alcohol  and  ether,  dried  thoroughly  and  mounted  in  hard  balsam.  This  is 
accomplished  by  placing  a  small  bit  of  hard  balsam  on  a  slide,  melting,  pushing  a 
bit  of  the  bone  into  the  hot  balsam,  covering  and  cooling  as  quickly  as  possible. 
The  object  of  the  hard  balsam  and  quick  cooling  is  to  prevent  the  balsam  running 
into  the  lacunas  and  canaliculi  and  obscuring  them  by  its  transparency.  The  air 
imprisoned  in  the  lacuna?  and  canaliculi  causes  them  to  appear  black  when  viewed 
by  reflected  light. 

(2)'  The  structure  of  the  bone  cell  is  best  studied  in  sections  of  decalcified  bone 
which  has  first  been  carefully  fixed.     (See  technic  1,  p.  156.) 

9.  Neuroglia. 

This  peculiar  form  of  connective  tissue  is  confined  entirely  to  the 
central  nervous  system  and  is  most  conveniently  studied  in  connec- 
tion with  nervous  tissue  (see  page  11 1). 


n 


■ 


CHAPTER    IV. 
THE    BLOOD. 

Blood  is  best  considered  as  a  tissue,  the  intercellular  substance 
of  which  is  fluid.  This  fluidity  of  the  intercellular  substance  allows 
the  formed  elements  or  cells  to  move  about  freely,  so  that  there  is 
not  the  same  definite  and  fixed  relation  between  cells  and  intercellu- 
lar substance  as  in  other  tissues. 

The  formed  elements  of  the  blood  are  :  (i)  Red  blood  cells  (red 
blood  corpuscles,  erythrocytes);  (2)  white  blood  cells  (colorless  cor- 
puscles— leucocytes);  (3)   blood  platelets  (thrombocytes). 

1.   Red  blood   cells  (erythrocytes)   (Fig.  45,  /,  2,  J)  are  in  man 
non-nucleated  circular  discs.     Their  average  diameter  is  about  7.5  y, 
their    thickness    2   y.    at   the    thin   centre. 
They  are  biconcave,  with   rounded   edges.       { 
Seen  on  the  flat,  the  difference  in  thickness  t  - 

between  centre  and  periphery  is  evidenced 
by  the  difference  in  refraction  (Fig.  45,  /). 
Seen  on   edge,  the  shape   resembles  that       w 
of  a  dumbbell  (Fig.  45,  2).      Singly  or  in 
small  numbers,  red  blood  cells  have  a  pale      ,    <s\l       .£&§*I$S      ^B 


straw  color.      Redness  of  the  cells  is  ap-  WM 

parent  only  when   they  are  seen  in    large 

Fig.  45-— Cells  from  Human  Blood. 

numbers.      If    fresh    blood    be    allowed  to      x  600.    (Technic2, P.  9o.)   /,  Red 
stand  for  a  moment,  the  red  cells  are  seen      ^00*  ce;!  seen  on  fl/l;  3'  re* 

blood  cell   seen  on  edge  ;  3,  red 

to  adhere  to  one  another  by  their  flat  sur-      Wood  ceils  forming  rouleaux; 

r  r  .  ,_.  4,  4,   small    and  large    Ivmpho- 

faces,    forming    rows    or    rouleaux    (Fig.      cytes.  5i   mononuclear'  ieuCo- 

a  r      o\  cyte  ;   6,  transitional  leucocyte; 

'  7,  polymorphonuclear  leucocyte, 

Subjected  tO  the  USUal  technic,  the  red        containing     neutrophil      gran- 

i  i         1           11                           1  t>       ^1             ules  ;   S,  polvnuclear    leucocvte, 

blood  cell  appears  homogeneous.     Bv  the     „„', .  )„„  '     ,„„„>,,,«,      '„ 

fit  o  j  containing      eosmophne      gran- 

USe    of     special     methods,     this    apparently       tiles;  9,  mononuclear  leucocyte, 

containing  basophile  granules. 

homogeneous  substance  can   be  separated 

into   (a)  a  color-bearing  proteid — hcemoglobin,  and   (b)  a  stroma,  the 

latter  representing  the  protoplasm  of  the  cell.      It  is  the  haemoglobin 

S5 


86  THE   TISSUES. 

which  gives  color  to  the  corpuscles.  Haemoglobin  is  a  complex 
proteid,  and  is  held  in  solution  or  in  suspension  in  the  stroma. 

The  red  blood  cells  are  soft  and  elastic,  and  are  easily  twisted 
to  accommodate  themselves  to  the  smallest  capillaries. 

The  red  blood  cell  is  extremely  susceptible  to  changes  in  the 
plasma.  Thus  even  slight  evaporation  of  the  plasma  results  in 
osmosis  between  the  now  denser  surrounding  fluid  and  the  contents 
of  the  cell.  This  causes  fluid  to  leave  the  cell,  with  the  result  that 
the  latter  becomes  spheroidal  and  irregularly  shrunken,  with  minute 
knob-like  projections  from  its  surface.  This  is  known  as  crenation 
of  the  red  cell.  The  addition  of  water  to  blood,  thus  decreasing  the 
specific  gravity  of  the  plasma,  has  the  opposite  effect,  resulting  in 
swelling  of  the  cell.  It  also  causes  solution  of  the  haemoglobin, 
which  leaves  the  cell,  the  latter  then  appearing  colorless.  Dilute 
acetic  acid  causes  swelling  and  fading  of  the  red  cells,  with  the  for- 
mation of  prismatic  crystals  of  haemoglobin. 

The  red  blood  cells  number  about  5,000,000  per  cubic  millimetre 
of  blood. 

2.  White  blood  cells  (leucocytes)  (Fig.  45,  4.  to  9  inclusive)  are 
colorless  nucleated  structures  which  have  a  generally  spherical  shape, 
but  which  are  able  to  change  their  shape  on  account  of  their  powers 
of  amoeboid  movement.  They  have  a  diameter  of  from  5  to  10  //, 
and  are  much  less  numerous  than  the  red  cells,  the  proportion  being 
about  one  white  cell  to  from  three  hundred  to  six  hundred  red  cells. 
This  proportion  is,  however,  subject  to  wide  variation. 

Leucocytes  may  be  classified  as  follows :  {a)  Lymphocytes ;  {b) 
mononuclear  leucocytes;  (c)  transitional  leucocytes;  (d)  polymor- 
phonuclear or  polynuclear  leucocytes. 

(a)  Lymphocytes  (Fig.  45,  4). — These  vary  in  diameter  from  5 
to  8  ',)■,  and  are  sometimes  subdivided  into  small  lymphocytes  and 
large  lymphocytes.  The  nucleus  is  spherical,  stains  deeply,  and  al- 
most completely  fills  the  cell,  the  cytoplasm  being  confined  to  a  nar- 
row zone  around  the  nucleus.  Lymphocytes  constitute  about  20  per 
cent  of  the  white  blood  cells. 

(/>)  Mononuclear  leucocytes  (Fig.  45,  5  and  9)  are  of  about 
the  same  size  as  large  lymphocytes.  The  nucleus,  however,  stains 
more  faintly  and  is  smaller,  while  the  cytoplasm  is  greater  in  amount. 
From  2  per  cent  to  4  per  cent  of  the  white  cells  are  mononuclear 
leucocytes. 


THE  BLOOD.  87 

{c)  Transitional  leucocytes  (Fig.  45,  <5 )  occur  in  about  the 
same  numbers  as  the  preceding,  and  are  of  about  the  same  size. 
There  is  relatively  more  cytoplasm,  and  the  nucleus,  instead  of  being 
spherical,  is  crescentic  or  horseshoe  or  irregular  in  shape.  These 
cells  represent  a  transitional  stage  between  the  mononuclear  and  the 
polymorphonuclear  and  polynuclear  varieties. 

(d)  Polymorphonuclear  and  polynuclear  leucocytes  (Fig. 
45,  /,  8)  constitute  about  70  per  cent  of  the  white  blood  cells.  Their 
size  is  about  the  same  as  that  of  the  mononuclear  form,  but  they  are 
somewhat  more  irregular  in  shape.  The  appearance  of  the  nucleus 
is  characteristic.  In  the  polymorphonuclear  form  the  nucleus  con- 
sists of  several  round,  oval,  or  irregular  nuclear  masses  connected 
with  one  another  by  cords  of  nuclear  substance.  These  cords  are 
frequently  so  delicate  as  to  be  distinguished  with  difficulty.  The 
polynuclear  form  is  derived  from  the  polymorphonuclear  by  breaking 
down  of  the  connecting  cords,  leaving  several  separate  nuclei  or 
nuclear  segments. 

The  protoplasm  of  leucocytes  is  granular,  and  these  granules  pre- 
sent very  definite  reactions  when  subjected  to  certain  aniline  dyes. 

Aniline  dyes  may  be  divided  into  acid,  basic,  and  neutral,  accord- 
ing to  whether  the  coloring  matter  is  an  acid,  a  base,  or  a  combina- 
tion of  an  acid  and  a  base. 

Upon  the  basis  of  their  reaction  to  these  dyes,  Ehrlich  divides 
these  granules  into  five  groups,  which  he  designates  by  the  first  five 
letters  of  the  Greek  alphabet. 

«- Granules  {acidopJiilc,  or,  because  the  most  common  acid  dye 
used  is  eosin,  eosinophile — Fig.  45,  8).  These  are  coarse,  sharply 
defined  granules  which  stain  intensely  with  acid  dyes.  Eosinophile 
cells  are  mainly  of  the  polynuclear  and  polymorphonuclear  types. 
More  rarely  transitional  forms  contain  eosinophile  granules.  They 
are  actively  amoeboid.  Eosinophile  cells  constitute  from  1  per  cent 
to  4  per  cent  of  the  leucocytes  of  normal  blood.  Under  certain 
pathological  conditions  the  number  of  eosinophile  leucocytes  is 
greatly  increased. 

,3- Granules  (amphophile).  These  are  very  fine  granules,  which 
react  to  both  acid  and  basic  dyes.  ,3-Granules  are  not  found  in  nor- 
mal human  blood.  They  are  found  in  the  blood  cells  of  some  of  the 
lower  animals. 

^-Granules  ipasophile)  are  small  granules  which  stain  with  basic 


88  THE    TISSUES. 

dyes.  They  occur  in  the  so-called  Mastzellen,  which  are  of  rare 
occurrence  in  normal  blood.  They  are  present  in  certain  pathologi- 
cal conditions,  and  are-found  normally  in  the  blood  cells  of  some  of 
the  lower  animals,  and  in  some  of  the  cells  of  connective  tissue. 

"-Granules  {basophile)  are  small  granules,  which  stain  with  basic 
dyes  (Fig.  45,  9).  They  are  found  mainly  in  the  mononuclear 
leucocytes. 

^-Granules  (ueutrophitc)  react  to  mixtures  of  acid  and  basic  dyes. 
£-Granules  are  the  most  common  of  all  granules,  occurring  in  most  of 
the  polynuclear  and  polymorphonuclear  forms,  being  thus  present  in 
about  68  per  cent  of  all  white  blood  cells  (Fig.  45,  y). 

Through  their  powers  of  amoeboid  movement  leucocytes  are  able 
not  only  to  pass  through  the  walls  of  the  vessels — diapcdesis — and 
out  into  the  tissues,  but  to  wander  about  more  or  less  freely  in  the 
tissues.  Both  inside  and  outside  of  the  vessels  the  leucocytes  have 
an  important  function  to  perform  in  the  taking  up  and  disposal  of 
waste  and  foreign  particles.  This  is  known  as  phagocytosis,  and  the 
cells  thus  engaged  are  known  as  phagocytes.  Phagocytosis  plays  an 
extremely  important  role  both  in  normal  and  in  certain  pathological 
processes. 

3.  The  blood  platelets  (thrombocytes)  are  minute  round  or  oval 
bodies  about  2  ;>.  in  diameter.  They  are  clear  (colorless),  and  are 
described  by  some  as  containing  chromatin  granules,  by  others  as 
having  distinct  nuclear  structures.  They  may  be  separated  by  the 
action  of  a  10-per-cent  saline  solution  into  two  elements. — one  hya- 
line, the  other  granular.  They  are  said  to  possess  amoeboid  properties 
and  to  be  concerned  in  the  coagulation  of  the  blood.  They  number 
about  200,000  per  cubic  millimetre. 

Development  of  the  Blood. 

At  an  early  stage  of  embryonic  development  certain  mesoblastic 
cells  of  the  area  vasculosa,  which  surrounds  the  embryo,  become 
arranged  in  groups  known  as  blood  islands.  It  is  from  these 
"  islands  "  that  both  blood  and  blood-vessels  develop.  The  periphe- 
ral cells  arrange  themselves  as  the  primitive  vascular  wall,  within 
which  the  central  cells  soon  become  free  as  the  first  blood  corpuscles. 
By  union  of  the  blood  islands,  vascular  channels  are  formed,  inside  of 
which  are  the  developing  blood  cells.     At  this  stage  the  formed  ele- 


THE  BLOOD.  89 

ments  of  blood  consist  almost  wholly  of  nucleated  red  cells.  These 
undergo  mitotic  division  and  multiply  within  the  vessels.  Two 
views  are  held  in  regard  to  the  manner  in  which  the  embryonic  nu- 
cleated red  cell  gets  rid  of  its  nucleus  in  becoming  the  non-nucleated 
red  cell  of  the  adult.  According  to  one  the  nucleus  is  absorbed 
within  the  cell ;  according  to  the  other  the  nucleus,  as  a  whole,  is 
extruded. 

In  early  embryonic  life  especially  active  proliferation  of  red  cells 
occurs  in  the  blood-vessels  of  the  liver.  This  has  led  to  the  consider- 
ing of  the  liver  as  a  blood-forming  organ.  The  liver  cells  themselves, 
however,  take  no  actual  part  in  the  formation  of  blood  cells,  the  blind 
pouch-like  venous  capillaries  of  the  liver,  with  their  slow-moving  blood 
currents,  merely  furnishing  a  peculiarly  suitable  place  for  cellular  pro- 
liferation. Before  birth  the  splenic  pulp  and  bone  marrow  become 
blood-forming  organs.  In  the  adult  the  bone  marrow  is  probably 
under  normal  conditions  the  main  if  not  the  sole  seat  of  red-cell  for- 
mation. 

During  fcetal  life  the  number  of  nucleated  red  cells  constantly 
diminishes  while  the  number  of  non-nucleated  red  cells  increases. 
At  birth  there  are  usually  but  few  nucleated  red  cells  in  the  general 
circulation,  although  even  in  the  adult  they  are  always  found  in  the 
red  bone  marrow. 

The  earliest  embryonic  blood  contains  no  white  cells. 

The  origin  of  the  leucocytes  is  not  well  understood.  It  seems 
probable  that  the  earliest  leucocytes  are  derived  like  the  red  cells 
from  the  cells  of  the  blood  islands  of  the  area  vasculosa.  Later  they 
are  formed  in  widely  distributed  groups  of  cells,  lymph  nodules, 
which  are  found  in  various  tissues  and  organs.  These  cells  enter 
the  circulation  as  lymphocytes.  According  to  some,  the  mononuclear, 
transitional,  polymorphonuclear  and  polynuclear  forms  are  later  stages 
in  the  development  of  these  cells.  According  to  others,  the  poly- 
morphonuclear and  polynuclear  forms  are  derived  from  the  myelo- 
cytes of  bone  marrow. 

The  origin  of  the  blood  platelets  is  not  known.  It  is  possible 
that  they  represent  extrusion  products  of  the  blood  cells. 

TECHNIC. 

(1)  Fresh  Blood.— Prick  a  finger  with  a  clean  needle.  Touch  the  drop  of  blood 
to  the  centre  of  the  slide  and  cover  quickly.     For  immediate  examination  of  fresh 


90  THE    TISSUES. 

blood  no  further  preparation  is  necessary.     Evaporation  may  be  prevented  by 
cementing  or  by  smearing  a  rim  of  vaseline  around  the  cover-glass. 

(2)  Blood  Smears. — From  the  same  or  a  second  prick  take  up  a  drop  of  blood 
along  the  edge  of  a  mounting  slide.  Quickly  place  the  edge  against  the  surface  of 
a  second  slide  and  draw  the  edge  across  the  surface  in  such  a  manner  as  to  leave  a 
thin  film  or  smear  of  blood.  Allow  the  smear  to  become  perfectly  dry  and  stain 
by  technic  7,  p.  24.  By  this  method  the  acidophile  granules  are  stained  red, 
basophile  granules  purple,  and  neutrophile  granules  a  reddish-violet. 

(3)  Good  results  may  also  be  obtained  by  fixing  the  dried  smear  for  half  an 
hour  in  equal  parts  alcohol  and  ether  and  staining  first  in  a  strong  alcoholic  solu- 
tion of  eosin,  then  in  a  rather  weak  aqueous  solution  of  methylene  blue. 


CHAPTER   V. 

MUSCLE    TISSUE. 

While  protoplasm  in  general  possesses  the  property  of  contrac- 
tility, it  is  in  muscle  tissue  that  this  property  reaches  its  highest  de- 
velopment.    Moreover,  in  muscle  this  contractility  is  along  definite 


FIG.  46. — Isolated  Smooth  Muscle  Cells  from  Human  Small  Intestine.  X  400.  (Technic  1, 
p.  99.)  Rod-shaped  nucleus  surrounded  by  area  of  finely  granular  protoplasm;  longi- 
tudinal striations  of  cytoplasm. 

directions,  and  is  capable  of  causing  motion,  not  only  in  the  cell  itself, 
but  in  structures  outside  the  cell. 

Muscle  may  be  classified  as  :  (i)  Involuntary  smooth  muscle ;  (2) 
voluntary  striated  muscle ;  (3)  involuntary  striated  muscle  or  heart 
muscle. 

1.  Involuntary  Smooth  Muscle. — This  consists  of  long  spindle- 
shaped  cells  (Fig.  46) .    The  length  of  the  cell  varies  from  30  to  200  ;x, 


B 


Fig.  47  —Apparent  Intercellular  Bridges  of  Smooth  Muscle.  A,  From  longitudinal  section  of 
intestine  of  guinea-pig  ;  B,  from  transverse  section  of  intestine  of  rabbit.  X  420.  a.  Nerve 
cell  ;  d,  end  of  muscle  cell.     (Stohr.) 

its  width  from  3  to  8  :>,  except  in  the  pregnant  uterus,  where  the  cells 
frequently  attain  a  much  greater  size.     At  the  centre  of  the  cell,  which 

91 


92  THE   TISSUES. 

is  its  thickest  portion,  is  a  long  rod-shaped  nucleus  surrounded  by  an 
area  of  finely  granular  cytoplasm.  The  rest  of  the  cytoplasm  shows 
delicate  longitudinal  striations,  which  probably  represent  a  longitu- 
dinal arrangement  of  the  spongioplasm.  The  cells  are  united 
by  a  small  amount  of  cement  substance.  Intercellular  "bridges" 
similar  to    those  connecting   epithelial   cells   have  been    described 

(Fig-  47)- 

Smooth  muscle  cells  may  be  arranged  in  layers  of  considerable 
thickness,  the  cells  having  a  definite  direction,  as  in  the  so-called 
"musculature"  of  the  intestine  (Fig.  48).  In  such  masses  of 
smooth  muscle  the  cells  are  separated  into  groups  or  bundles  by 
connective  tissue.  Smooth  muscle  cells  may  be  arranged  in  a  sort 
of  network,  the  cells  crossing  and  interlacing  in  all  directions,  as  in 

d 


SP^PS-SW'";'  ~™-'K%'--.~;y>pi&i&$ 


'  '..-.'.•-'■".:V,-J''"-'>.W" 


''■- 


FIG.  48. — Smooth  Muscle  from  Longitudinal  Section  of  Cat's  Small  Intestine,  showing'  Por- 
tions of  Inner  Circular  and  Outer  Longitudinal  Muscle  Coats  with  Intervening  Connec- 
tive Tissue.  X  350.  (Technic  3,  p.  100.)  a,  Transversely  cut  cells  of  inner  circular  layer  ; 
in  comparatively  few  has  the  plane  of  section  passed  through  the  nucleus;  b,  longitudi- 
nally cut  cells  of  outer  longitudinal  layer.  In  many  of  the  cells  the  plane  of  section  has 
not  passed  through  the  nucleus;  c,  intermuscular  septum  (connective  tissue);  rf,  small 
artery. 

the  wall  of  the  frog's  bladder.  Again,  they  may  be  scattered  in 
small  groups  or  singly  among  connective-tissue  elements,  as  in  the 
villi  of  the  small  intestine. 

2.  Voluntary  Striated  Muscle. — This  consists  of  cylindrical 
fibres  from  30  to  120  [t  in  length  and  from  10  to  60  //  in  di- 
ameter. 

Each  muscle  fibre  consists  of  (a)  a  delicate  sheath,  the  sarco- 
lemma,  enclosing  (/;)  the  muscle  substance  proper,  in  which  lie  (c) 
the  muscle  nuclei. 

The  sarcolemma  is  a  clear,  apparently  structureless,  membrane, 


MUSCLE    TISSUE. 


93 


which  adheres  so  closely  to  the  underlying  muscle  substance  as  to  be 
indistinguishable  in  most  preparations.  In  teased  specimens  it  may 
frequently  be  seen  at  the  torn  ends  of  the 
fibres  (Fig.  49). 

The  muscle  substance  consists  of  JibrillcB  and 
sarcoplasm,  and  shows  two  sets  of  striations 
(Fig.  50),  longitudinal  striations  and  cross  stria- 
tions. The  longitudinal  striations  are  due  to 
parallel  running  ultimate  fibrillse,  of  which  the 
muscle  fibre  is  composed.  These  fibrillar  are 
united  by  a  minute  amount  of  interfibrillar 
cement  substance.  The  transverse  striations 
appear  in  the  unstained  fibre  examined  by  re- 
flected light  as  alternate  light  and  dark  bands 
(Figs.  50  and  51).  The  light  band  is  composed 
of  a  singly  refracting  (isotrophic)  substance, 
the  dark  band  of  a  doubly  refracting  (anisotro- 
phic)  substance.  Through  the  middle  of  the 
light  band  runs  a  fine  dark  (anisotrophic)  line 
{Krause' ' s  line),  while  an  even  finer  light  (iso- 
trophic) line  (He/iscjt's  line)  runs  through  the 
middle  of  the  dark  band.  As  both  dark  and 
light  substances  run  through  the  entire  thick- 
ness of  the  fibre,  they  in  reality  constitute  discs 
of  muscle  substance  (Fig.  51).  By  means  of 
certain  chemicals  these  discs  may  be  separated, 
the  separation  taking  place  along  the  lines  of 
Krause.  Each  "muscle  disc"  thus  consists  of 
that  portion  of  a  fibre  included  between  two 
adjacent  lines  of  Krause  and  is  composed  of  a 
central  dark  disc,  and  on  either  side  one-half  of 
each  adjacent  light  disc.  A  muscle  fibre  is 
thus  seen  to  be  divisible  longitudinally  into 
ultimate  fibrillcB,  transversely  into  muscle  discs. 
What  is  known  as  the  sarcous  element  of  Bozv- 
mau  is  that  portion  of  a  single  fibrilla  which 
is  included  in  a  single  disc,  i.e.,  between  two 
adjacent  lines  of  Krause  (Fig.  51). 

The  sarcoplasm    is    not    evenly  distributed 


TTf 


FIG.  49.—  Semidiagramma- 
tic  Drawing  of  Parts  of 
two  Muscle  Fibres  which 
have  been  broken,  show- 
ing- the  relations  be- 
tween Muscle  Substance 
Proper  and  Sarcolemma. 
(Ranvier.)  ;//,  a,  Retract- 
ed ends  of  muscle  sub- 
stance, between  which  is 
seen  the  sarcolemma 
with  several  adherent 
muscle  nuclei  ;  B,  thin 
layer  of  muscle  sub- 
stance which  has  adhered 
to  the  sarcolemma  ;  ;/, 
muscle  nucleus  ;  J,  sar- 
colemma; fl,  space  be- 
tween sarcolemma  and 
muscle  substance. 


94 


THE    TISSUES. 


throughout  the  fibre.  On  cross  section  irregular  trabecular  of  sar- 
coplasm  are  seen  extending  in  from  the  sarcolemma  (Fig.  52). 
These  separate  the  fibrillar  into  bundles,  the  muscle  columns  of 
Kbllikcr.  A  transverse  section  of  one  of  these  columns  presents 
the  appearance  of  a  network  of  sarcoplasm  and  of  interfibrillar 
cement  substance  enclosing  the  fibrillae.     This  appearance  is  known 

as    Cohnheim  s.  field  (Figs.  51    and 

52). 

The  contractile  clement   of  the 

fibre,  the  fibrillce,  is  anisotrophic, 


I b 


Fig. 


Fig.  51. 


Fig.  50.— Portion  of  Striated  Voluntary  Muscle  Fibre.  X  350.  (Technic  4,  p.  100.)  The  fibre  is 
seen  to  be  marked  transversely  by  alternate  light  and  dark  bands.  Through  the  centre 
of  the  light  band  is  a  delicate  dark  line  (Krause's  line);  through  the  centre  of  the  dark 
band  a  fine  light  line  indicates  Henson's  line.  The  black  line  outlining  the  fibre  repre- 
sents the  sarcolemma.     a,  Fibrillar  ;  b,  muscle  nucleus  ;  c,  Krause's  line  ;  d,  Henson's  line. 

FIG.  51.— Diagram  of  Structure  of  a  Muscle  Column  of  Kolliker.  The  appearance  presented 
by  the  cross-cut  muscle  column  ^Cohnheim's  field,  a,  Muscle  fibrillae  ;  b,  sarcous  element ; 
c,  Krause's  line,  d,  Hensen's  line  ;  e,  Cohnheim's  field  ;  /",  muscle  disc. 


the  sarcoplasm  isotrophic;  the  former,  therefore,  appears  dark,  the 
latter  light  by  reflected  light.  Upon  this  is  based  Rollet's  theory 
of  the  structure  of  the  striated  muscle  fibre  (Fig.  53).  According  to 
this  theory,  each  fibrilla  consists  of  a  number  of  rod-shaped  segments 
joined  end  to  end.  Each  segment  consists  of  a  thicker  central  por- 
tion, which  tapers  almost  to  a  point  where  it  joins  the  next  adjacent 
segment.      The  point  of  union  is  marked  by  a  minute  globular  swell- 


MUSCLE    TISSUE. 


95 


ing.  Between  the  fibrillar  is  the  semi-fluid  sarcoplasm.  In  the  for- 
mation of  a  fibre  similar  parts  of  each  fibril  segment  lie  in  the  same 
transverse  plane.  The  thicker  portions  lying  side  by  side  form  the 
dark  disc  in  which  there  is  comparatively  little  sarcoplasm.  The 
attenuated  portions,  with  their  relatively  large  amount  of  sarcoplasm, 
form  the  light  disc.  The  row  of  globular  swellings  forms  the  line 
of  Krause. 

Two  varieties  of  striated  voluntary  muscle  fibres  are  distinguished, 
white  fibres  and  red  fibres.  The  difference  between  the  two  is  due 
to  the  amount  of  sarcoplasm — the 
red  fibres  being  rich  in  sarcoplasm, 
the  white  fibres  poor.  Red  fibres 
contract  less  rapidly  than  white, 
but  are  less  easily  fatigued.  In 
man  white  fibres  are  in  the  large 
majority,  red  fibres  never  occurring 


Fig.  52. 


d  c 


Fig. 


Fig.  52. — Semidiagrammatic  Drawing-  of  Transverse  Section  of  a  Voluntary  Muscle  Fibre, 
showing  Sarcolemma;  sarcoplasm  separating  fibrils  into  bundles,  each  bundle  constitut- 
ing a  muscle  column  of  Kolliker  and  the  appearance  of  its  cross  cut  end  being  Cohnheim's 
field,     a,  Sarcoplasm  ;  l\  Cohnheim's  fields  ;  c,  sarcolemma. 

FIG.  53.— Diagram  representing  Rollet's  Theory  of  the  Structure  of  a  Voluntary  Muscle 
Fibre,     a,  Dark  disc  ;   b,  light  disc  ;  c,  sarcoplasm  ;  d,  fibrilla  ;  e,  Krause's  line. 


alone,  but  mingled  with  white  fibres  in  some  of  the  more  active 
muscles,  such  as  those  of  respiration  and  mastication.  In  some  of 
the  lower  animals  are  found  muscles  made  up  wholly  of  red  fibres. 

Muscle  fibres  ending  within  the  substance  of  a  muscle  have 
pointed  extremities.  Where  muscle  fibres  join  tendon,  the  fibre 
ends  in  a  rounded  or  blunt  extremity,  the  sarcolemma  being  continu- 
ous with  the  tendon  fibres  (Figs.   54  and  55). 


96 


THE   TISSUES. 


Muscle  fibres  are  usually  unbranched.      In  some  muscles — e.g., 
those  of  the  tongue  and  of  the  eye — anastomosing"  branches  occur. 
When  muscle  fibres  end  in  mucous  membranes 
— e.g.,  the  muscle  fibres  of  the  tongue, — their 
terminations  are  often  branched. 

Muscle  fibres  are  multinuclear,  some  of  the 
larger  fibres  containing  a  hundred  or  more 
nuclei.  In  the  white  fibres  the  nuclei  are 
situated  at  the  periphery  just  beneath  the  sarco- 
lemma.  In  red  fibres  they  are  centrally  placed. 
3.  Involuntary  Striated  Muscle  (Heart 
Muscle). — This  occupies  an  intermediate  posi- 
tion, both  morphologically  and  embryologically, 
relative  to  smooth  muscle  and  to  striated  vol- 
:^~"  ~  :^SA  untary  muscle.      Like  the  former,   it   is    com- 

,zl   ._;  -j  posed    of   cells.      Like    the    latter,    it    is    both 

■  --    —      7 'i  longitudinally  and  transversely  striated.      Heart- 

muscle  cells  are  short,  thick  cylinders.     These 
|gp  are    joined    end    to    end    to  form    long    fibres. 

I  S0.        ; |n ':'.-  By  means  of  lateral   branches  the  cells  of  one 

'_.•    £r   ■'  fibre  anastomose  with  cells  of  adjacent  fibres. 

Each  heart-muscle  cell  usually  contains  one 
nucleus ;  some  cells  contain  several  nuclei. 
While  there  is  no  distinct  sarcolemma,  the  sar- 
coplasm  is  more  abundant  at  the  surface  of  the 
cell,  thus  giving  much  the  appearance  of  an 
enclosing  membrane.  The  amount  of  sarco- 
plasm  throughout  the  cell  is  large.  Around 
the  nucleus  is  an  area  of  sarcoplasm  free  from 
fibrillar.  This  area  often  extends  some  distance 
toward  the  ends  of  the  cell. 

The  striations  of  heart  muscle  are  less  dis- 
tinct than  are  those  of  voluntary  muscle.  Ac- 
cording to  McCallum,  they  represent  very  sim- 
ilar structures.  The  longitudinal  striations 
indicate  fibrilUe  united  by  cement  substance. 
From  the  central  mass  of  sarcoplasm  which 
surrounds  the  nucleus,  strands  radiate  toward 
the    periphery.      These    strands,   anastomosing, 


! " " '     iiii 


^Krfe 


wMM 

['.'it 

Fin.  54.  Semidiagram- 
matic  Illustration  of 
Kndings  of  Muscle  Fi- 
bres within  a  Muscle 
and  in  Tendon.  (Gage.) 
a.  Tapering  end  of  fibre 
terminating  within  the 
muscle;  the  lower  end 
of  the  central  fibre 
shows  the  same  method 
of  termination  ;  c,  c. 
each  fibre  terminates 
above  in  pointed  intra- 
muscular ending,  below 
in  blunt  ending  con- 
nected with  tendon. 


MUSCLE    TISSUE. 


97 


separate  the  fibrillar  into  columns,  the  muscle  columns  of  Kollikcr. 
In  cross  section  these  present  the  appearance  described  under  vol- 
untary muscle  as  Cohnheim  s  fields.  The  disposition  of  the  sarco- 
plasm,  extending  outward  from  the  region  of  the  nucleus  like  the 
spokes  of  a  wheel,  gives  to  the  cross  section  a  characteristic  radiate 
appearance  (Fig.  57).  The  transverse  markings  represent,  as  in  vol- 
untary muscle,  alternate  light  and  dark  discs.  Through  the  middle 
of  the  light  disc  can  be  seen  the  membrane  of  Krause.  McCallum 
describes  Krause's  membrane  as  belonging  not  only  to  the  fibrillar 
element,  but  also  to  the  sarcoplasm.  The  latter  he  describes  as 
further  subdivided  by  membranes,  which  are  transversely  continuous 


r'l 


Fig.  55.  Fig.  56. 

FlG.  55.— Two  Muscle  Fibres  from  Upper  End  of  Human  Sartorius,  to  show  connection  of 
muscle  and  tendon.     X  350.     (Gage.)     ?n,  Muscle  fibres;  /,  tendon  fibres. 

FlG.  56. — Muscle  Cells  from  the  Human  Heart  (technic  6,  p.  100),  showing  lateral  branches 
and  lines  of  union  between  cells.     X  500. 


with  Krause's  membranes,  into  minute  discs.  The  centre  of  the 
cell  around  the  nucleus  is  wholly  composed  of  these  little  discs  of 
sarcoplasm. 

McCallum  describes  two  appearances  which  the  lines  of  union 
between  the  muscle  cells  present.  In  one  each  fibrilla  shows  a 
thickening  at  the  cement  line,  from  which  one  or  more  delicate  fila- 
ments cross  the  cement  to  unite  with  similar  filaments  from  an  oppo- 


98  THE   TISSUES. 

site  fibrilla.  In  the  other  form  of  union  the  cement  substance  is 
crossed  by  intercellular  bridges  similar  to  those  described  under 
epithelium. 

Recent  investigations  tend  to  prove  that  what  have  been  described 
as  heart-muscle  cells  are  not  separate  units,  but  that  heart  muscle  is 
a  syncytial  tissue,  each  cell  representing  only  a  growth  segment  of 
the    whole    muscle    fibre.      The    occurrence   of    non- nucleated    seg- 

a  c  b 

!  ;  ! 


m 


§/© 


Fig.  57. — Section  of  Heart  Muscle.  X  350.  (Technic  7,  p.  100.)  a,  Cells  cut  longitudinally;  bT 
cells  cut  transversely  (only  three  nuclei  have  been  included  in  the  plane  of  section)  ;  c, 
connective-tissue  septum. 

ments  and  the  fact  that  the  longitudinal  fibrillar  are  described  by 
some  observers  as  passing  uninterruptedly  through  the  "  intercellu- 
lar "  cement  substance  favor  this  view.  On  the  other  hand,  the  ease 
with  which  heart  muscle  may  be  separated  into  cells,  especially  in 
young  animals  and  in  the  lower  vertebrates,  and  the  definite  staining 
•reaction  which  the  intercellular  substance  gives  when  subjected  to 
the  action  of  silver  nitrate  are  in  favor  of  a  cellular  structure. 


Development  of  Muscle  Tissue. 

In  the  higher  animals  muscle  tissue,  with  the  single  exception  of 
the  sweat-gland  muscles  (page  51),  is  derived  wholly  from  mesoderm. 
Smooth  muscle  is  developed  from  the  mesenchyme,  while  heart  mus- 
cle and  voluntary  muscle  are  derived  from  the  mesothelium. 

The  smooth  muscle  cell  shows  the  least  differentiation.  In  be- 
coming a  smooth  muscle  cell  the  formative  cell  changes  its  shape,. 


MUSCLE    TISSUE.  99 

becoming  greatly  elongated,  while  at  the  same  time  its  spongioplasm 
is  arranged  as  longitudinally  disposed  contractile  fibrils. 

A  voluntary  muscle  fibre  is  a  highly  differentiated  multinuclear 
cell  or  syncytium.  Each  fibre  is  developed  from  a  single  cell  {myo- 
blast) of  one  of  the  embryonic  muscle  segments  or  myotonics.  These 
cells,  which  are  at  first  spherical,  become  elongated  and  spindle- 
shaped.  The  nucleus  is  at  this  stage  centrally  placed,  and  the 
spongioplasm  occurs  in  the  form  of  a  reticulum.  Regular  arrange- 
ment of  the  spongioplasm  first  appears  around  the  periphery,  while 
the  central  portion  of  the  cell  is  still  occupied  by  reticular  spongio- 
plasm and  the  nucleus.  The  fibrils  extend  toward  the  centre  until 
they  fill  the  entire  cell,  which  has  now  become  a  muscle  fibre.  Dur- 
ing this  process  of  fibrillation  the  nucleus  has  been  undergoing  mi- 
totic division,  and  the  new  nuclei  have  migrated  to  the  surface  and 
come  to  lie  just  beneath  the  sarcolemma.  The  cement  substance 
which  unites  the  fibrils,  as  well  as  the  larger  masses  of  sarcoplasm, 
represents  the  remains  of  still  undifferentiated  protoplasm  (hyalo- 
plasm). 

McCallum  describes  the  development  of  heart  muscle  in  the  pig 
as  follows  :  In  embryos  10  mm.  long  the  heart  muscle  consists  of 
closely  packed  spindle-shaped  cells,  each  containing  an  oval  nucleus. 
The  spongioplasm  is  arranged  in  the  form  of  a  network,  no  fibrils 
being  present.  In  embryos  25  mm.  long  the  shape  of  the  cell  re- 
mains unchanged,  but  on  cross  section  there  can  be  seen  around  the 
periphery  a  row  of  newly  formed  fibril  bundles  which  have  developed 
from  the  spongioplasm.  From  the  periphery  fibril  bundles  spread 
toward  the  centre.  In  embryos  70  mm.  long  the  heart-muscle  cell 
has  assumed  its  adult  shape  and  structure. 

Attention  has  already  been  called  (page  38)  to  the  spongio- 
plasm as  the  contractile  element  of  protoplasm.  It  is  to  be  noted 
that  in  the  development  of  muscle  no  new  element  appears,  the  con- 
tractile fibrillar  representing  nothing  more  than  a  specialisation  of 
the  already  contractile  spongioplasm. 

TECHNIC. 

(1)  Isolated  Smooth  Muscle  Cells. — Place  small  pieces  of  the  muscular  coat  of 
the  intestine  in  0.1-per-cent  aqueous  solution  of  potassium  bichromate,  or  in  30-per- 
cent alcohol  for  forty-eight  hours.  Small  bits  of  the  tissue  are  teased  thoroughly 
and  mounted  in  glycerin.  Nuclei  may  be  demonstrated  by  first  washing  the  tissue 
and  then  staining  for  twelve  hours  in  alum-carmine  (page  15).     This  is  poured  off, 


IOO  THE   TISSUES. 

the  tissue  again  washed  in  water  and  preserved  in  eosin-glycerin,  which  gives  a 
pink  color  to  the  cytoplasm. 

(2)  Potassium  hydrate  in  40-per-cent  aqueous  solution  is  also  recommended  as 
a  dissociater  of  smooth  muscle  cells.  Pieces  of  the  muscular  coat  of  the  intestine 
are  placed  in  this  solution  for  five  minutes,  then  transferred  to  a  saturated  aqueous 
solution  of  potassium  acetate  containing  i-per-cent  hydric  acetate  for  ten  minutes. 
Replace  the  acetate  solution  by  water,  shake  thoroughly,  allow  to  settle,  pour  off 
water,  and  add  alum-carmine  solution  (page  15).  After  twelve  hours'  staining, 
wash  and  transfer  to  eosin-glycerin. 

(3)  Sections  of  Smooth  Muscle. — Fix  small  pieces  of  intestine  in  formalin- 
Muller's  (technic  5,  p.  5)  or  in  Zenker's  fluid  (technic  9,  p.  6).  Thin  transverse  or 
longitudinal  sections  are  stained  with  hasmotoxylin-eosin  (technic  1,  p.  16).  and 
mounted  in  balsam.  As  the  two  muscular  coats  of  the  intestine  run  at  right  angles 
to  each  other,  both  longitudinally  and  transversely  cut  muscle  may  be  studied  in 
the  same  section. 

(4)  Striated  Voluntary  Muscle  Fibres. — One  of  the  long  muscles  removed  from 
a  recently  killed  animal  is  kept  in  a  condition  of  forced  extension  while  a  i-per- 
cent  aqueous  solution  of  osmic  acid  is  injected  into  its  substance  at  various  points 
by  means  of  a  hypodermic  syringe.  Fixation  is  accomplished  in  from  three  to  five 
minutes.  The  parts  browned  by  the  osmic  acid  are  then  cut  out  and  placed  in  pure 
glycerin,  in  which  they  are  teased  and  mounted. 

(5)  Sections  of  Striated  Voluntary  Muscle. — Fix  a  portion  of  a  tongue  in  forma- 
lin-Miiller's  fluid  or  in  Zenker's  fluid  (page  6).  Thin  sections  are  stained  with 
hajmatoxylin-picro-acid-fuchsin  (technic  3,  p.  16)  and  mounted  in  balsam.  As  the 
muscle  fibres  of  the  tongue  run  in  all  directions,  fibres  cut  transversely,  longitudi- 
nally, and  obliquely  may  be  studied  in  the  same  section.  The  sarcolemma,  the 
pointed  endings  of  the  fibres,  and  the  relation  of  the  fibres  to  the  connective  tissue 
can  also  be  seen. 

(6)  Isolated  heart-muscle  cells  may  be  obtained  in  the  same  manner  as  smooth 
muscle  cells  (see  technic  1). 

(■j)  Sections  of  Heart  Muscle. — These  are  prepared  according  to  technic  3, 
above).  By  including  the  heart  wall  and  a  papillary  muscle  in  the  same  section, 
both  longitudinally  and  transversely  cut  cells  are  secured.  The  stain  may  be  either 
hamiatoxylin-eosin  (technic  1,  p.  16),  or  hasmatoxylin-picro-acid-fuchsin  (technic 
3.  p.  16). 


CHAPTER    VI. 

NERVE    TISSUE. 
The  Neurone. 

In  most  of  the  cells  thus  far  described  the  protoplasm  has  been 
confined  to  the  immediate  vicinity  of  the  nucleus.  In  the  smooth 
muscle  cell  was  seen  an  extension  of  protoplasm  to  a  considerable 
distance  from  the  nuclear  region,  while  in  the  connective-tissue  cells 
of  the  cornea  the  protoplasmic  extensions  took  the  form  of  distinct 
processes.  Such  processes,  often  extending  long  distances  from  the 
cell  body  proper,  constitute  one  of  the  most  striking  features  of 
nerve-cell  structure.  It  is  these  processes  which  are  known  as  nerve 
fibres;  and  nerve  tissue  was  long  described  as  consisting  of  two  ele- 
ments, nerve  cells  and  nerve  fibres.  With  the  establishment  of  the 
unity  of  the  nerve  cell  and  the  nerve  fibre,  the  nerve  cell  with  its 
processes  was  recognized  as  the  single  structural  unit  of  nerve  tissue. 
This  unit  of  structure  is  known  as  a  neurone.  The  neurone  may  thus 
be  defined  as  a  nerve  cell  ivith  all  of  its  processes. 

In  the  embryo  the  neurone  is  developed  from  one  of  the  ectoder- 
mic  cells  which  constitute  the  wall  of  the  primitive  neural  canal. 
This  embryonic  nerve  cell,  or  neuroblast,  is  entirely  devoid  of  proc- 
esses. Soon,  however,  from  one  end  of  the  cell  a  process  begins  to 
grow  out.  This  process  is  known  as  the  axone  (axis-cylinder  process, 
neuraxone,  neurite).  Other  processes  appear,  also  as  outgrowths  of 
the  cell  body;  these  are  known  as  protoplasmic  processes  or  dendrites. 

Each  adult  neurone  thus  consists  of  a  cell  body,  and  passing  off 
from  this  cell  body  two  kinds  of  processes,  the  axis-cylinder  process 
and  the  dendritic  processes  (Fig.   58). 

I.  The  Cell  Body.  Like  most  other  cells,  the  nerve  cell  body 
consists  of  a  mass  of  protoplasm  surrounding  a  nucleus  (Fig.  59). 
Nerve  cell  bodies  vary  in  size  from  very  small  cell  bodies,  such  as 
those  found  in  the  granule  layers  of  the  cerebellum  and  of  the  olfac- 
tory lobe,  to  the  large  bodies  of  the  Purkinje  cells  of  the  cerebellum 
and  of  the  motor  cells  of  the  ventral  horns  of  the  cord,  which  are 


102 


THE    TISSUES. 


among  the  largest  in  the  body.     There  is  as  much  variation  in  shape 
as  in  size,  and  some  of  the  shapes  are  characteristic  of  the  regions  in 

which  the  cells  are  situated.  Thus  the 
bodies  of  the  cells  of  the  spinal  ganglia 
are  spheroidal ;  of  most  of  the  cells  of 
the  cortex  cerebri,  pyramidal ;  of  the 
cells  of  Purkinje,  pyriform  ;  of  the  cells 
of  the  ventral  horns  of  the  cord,  irreg- 
ularly stellate.     According  to  the  num- 


Fig.  58.  Fig.  59 

Fig.  58.— Scheme  of  Lower  Motor  Neurone.  The  cell  body,  protoplasmic  processes,  axone, 
collaterals,  and  terminal  arborizations  in  muscle  are  all  seen  to  be  parts  of  a  single  cell 
and  together  constitute  the  neurofte.  (Barker),  c,  Cytoplasm  of  cell  body  containing 
chromophilic  bodies,  neurofibrils,  and  perifibrillar  substance  ;  n,  nucleus  ;  7/',  nucleolus  ; 
d,  dendrites;  a  /i,  axone  hill  free  from  chromophilic  bodies;  ax,  axone  ;  sf,  side  fibril 
(collateral)  ;  ;//,  medullary  sheath  ;  11  R,  node  of  Ranvier  where  side  branch  is  given  off  ; 
si,  neurilemma  and  incisures  of  Schmidt ;  in',  striated  muscle  fibre  ;  tel,  motor  end  plate. 

PlG.  ,. — Large  Motor  Ganglion  Cell  from  Ventral  Horn  of  Spinal  Cord  of  Ox,  showing 
Chromophilic  Bodies.  (From  Barker,  after  von  Lenhossek.)  a,  Pigment  ;  /;,  axone  ; 
c,  axone  hill  ;  d,  dendrites. 


ber    of    processes    given    off,    nerve  cells   are    often   referred    to  as 
unipolar,  bipolar,  or  multipolar. 

The  nucleus  of  the  nerve  cell  (Fig.  59)  differs  in  no  essential 
from  the  typical  nuclear  structure.  It  consists  of  (1)  a  nuclear  mem- 
brane, (2)  a  chromatic  nuclear  network,  (3)  an  achromatic  nucleo- 
plasm, and  (4)  a  nucleolus. 


NERVE   TISSUE.  103 

The  cytoplasm  of  the  nerve  cell  consists  of  two  distinct  ele- 
ments :  (1)  Neurofibrils,  and  (2)  perifibrillar  substance.  In  most 
nerve  cells  a  third  element  is  present,  (3)  chromophilic  bodies. 

(1)  The  neurofibrils  are  extremely  delicate  fibrils  which  are  con- 
tinuous throughout  the  cell  body  and  all  of  its  processes.  Within 
the  body  of  the  cell  they  cross  and  interlace  and  probably  anastomose 
(Fig.  60). 

(2)  The  perifibrillar  substance  (Fig.  60)  is  a  fluid  or  semifluid 
substance  which  both   in   the  cell   body  and  in   the   processes   sur- 


■  Y.'V 

M 


m 


I 


§ 


■'■', 

A 

Fig.  60.  — Ganglion  Cells,  Stained  by  Bethe's  Method,  showing  Neurofibrils.  A,  Anterior  horn 
cells  (human)  ;  B,  cell  from  facial  nucleus  of  rabbit ;  C,  dendrite  of  human  anterior  horn 
cell  showing  arrangement  of  neurofibrils.     (Bethe.) 

rounds  and  separates  the  neurofibrils.  It  is  believed  by  some  to  be  like 
the  fibrils,  continuous  throughout  cell  body  and  processes,  by  others  to 
be  interrupted  at  certain  points  in  the  axone  (see  page  109). 


104 


THE    TISSUES. 


(3)  The  chromopkilic  bodies  (Fig.  59)  are  granules  or  groups  of 
granules  which  occur  in  the  cytoplasm  of  all  of  the  larger  and  of 
some  of  the  smaller  nerve  cells.  They  are  best  demonstrated  by 
means  of  a  special  technic  known  as  the 
method  of  Nissl  (page  28).  When  sub- 
jected to  this  technic,  nerve  cells  present 
two  very  different  types  of  reaction.  In 
certain  cells,  only  the  nuclei  stain.  Such 
cells  are  found  in  the  granule  layers  of  the 
cerebellum,  olfactory  lobe,  and  retina.  They 
are  known  as  caryochromes,  and  apparently 
consist  wholly  of  neurofibrils  and  perifibrillar 
substance.  Other  cells  react  both  as  to  their 
nuclei  and  as  to  their  cell  bodies,  to  the 
Nissl  stain.  These  cells  are  known  as 
somatochromes.  Taking  as  an  example  of 
this  latter  type  of  cell  one  of  the  motor 
cells  of  the  ventral  horn  of  the  cord  and 
subjecting  it  to  the  Nissl  technic,  we  note 
that  the  cytoplasm  is  composed  of  two  dis- 
tinct elements  :  (a)  a  clear,  unstained  ground 
substance,  and,  scattered  through  this,  (/;) 
deep  blue-staining  masses,  the  chromopkilic 
bodies  (Fig.  59).  These  bodies  are  granular 
in  character  and  differ  in  shape,  size, 
and  arrangement.  They  may  be  large 
or  small,  regular  or  irregular  in  shape, 
may  be  arranged  in  rows  or  in  an  ir- 
regular manner,  may  be  close  together, 
almost  filling  the  cell  body,  or  quite 
separated  from  one  another.  Present- 
ing these  variations  in  different  types 
of  cells,  the  appearance  which  the  chromophilic  bodies  present  in  a 
particular  type  of  cell  remains  constant,  and  has  thus  been  used  by 
Nissl  as  a  basrs  of  classification.1 

It  is  important  to  note  in  studying  the  nerve  cell  by  this  method 


Fig.  61. — Pyramidal  Cell  from  Cere- 
bral Cortex  of  Mouse.  (After  Ra- 
mon y  CajalJ  Golgi  cell  type  I.  d, 
Cell  body  giving  off  main  or  apical 
dendrite  ;  </,  main  dendrite  showing 
gemmules;  e,  axone  with  collater- 
als. Only  part  of  axone  is  included 
in  drawing. 


1  For  this  classification,  the-  significance  of  which  is  somewhat  doubtful,  the 
reader  is  referred  to  Barker,  "  The  Nervous  System  and  Its  Constituent  Neurones," 
p.  121. 


NERVE    TISSUE. 


105 


that  somatochrome  cells  of  the  same  type  frequently  show  marked 
variations  in  staining  intensity.  This  appears  to  depend  upon  the 
size  and  closeness  of  arrangement  of  the  chromophilic  bodies,  and 
this  again  seems  dependent  upon  changes  in  the  cytoplasm  connected 
with  functional  activity. 

In  cells  stained  by  Nissl's  method  the  cytoplasm  between  the 
chromophilic  bodies  remains  unstained  and  apparently  structureless, 
and  it  is  this  part  of  the  cytoplasm  that  corresponds  to  the  neuro- 
fibrils and  perifibrillar  substance. 

The  relation  which  the  appearance  of  the  Nissl-stained  cell  bears 
to  the  structure  of  the  living  protoplasm  is  still  undetermined.  Ac- 
cording to  some  investigators  the  Nissl  bodies  exist  as  such  in  the 
living  cell.      Others   believe  that  they  are  not  present   in  the  living 


FIG.  62.— Golgi  Cell  Type  II.  from  Cerebral  Cortex  of  Cat.  (Kolliker.)  .v,  Coarse  proto- 
plasmic processes  with  gemmules  easily  distinguishable  from  the  more  delicate,  smoother 
axone,  a.  The  latter  is  seen  breaking  up  into  a  rich  plexus  of  terminal  fibres  near  its  cell 
of  origin,  practically  the  entire  neurone  being  included  in  the  drawing. 


cell,  but  represent  precipitates  due  either  to  post-mortem  changes  or 
to  the  action  of  fixatives.  The  significance  of  the  Nissl  picture  from 
the  standpoint  of  pathology  lies  in  the  fact  that  when  subjected  to  a 
given  technic,  a  particular  type  of  nerve  cell  always  presents  the 
same  appearance,  and  that  this  appearance  furnishes  a  norm  for  com- 


106  THE   TISSUES. 

parison  with  cells  showing  pathological  changes,  and  which  have  been 
subjected  to  the  same  technic. 


Many  nerve  cells  contain  more  or  less  brownish  or  yellowish  pig- 
ment (Fig.  59).  This  pigment  is  not  present  in  the  cells  of  the  new- 
born, but  appears  in  increasing  amounts  with  age.  Its  significance 
is  not  known. 

II.  The  Protoplasmic  Processes  or  Dendrites. — These  have  a 
structure  similar  to  that  of  the  cell  body,  consisting  of  neurofibrils, 
perifibrillar  substance,  and  chromophilic  bodies  (Figs.  59  and  60). 
Dendrites  branch  dichotomously,  become  rapidly  smaller,  and  usu- 
ally end  at  no  great  distance  from  the  cell  body  (Figs.  61  and  62). 

III.  The  Axone. — This  differs  from  the  cell  body  and  dendrites  in 
that  it  contains  no  chromophilic  bodies  (Fig.  59),  consisting  wholly 
of  neurofibrils  and  perifibrillar  substance.  Not  only  is  it  entirely 
achromatic  itself,  but  it  always  takes  origin  from  an  area  of  the  cell 
body,  the  axone  hill  or  implantation  cone  (Fig.  59),  which  is  free  from 
chromophilic  bodies.  It  is  as  a  rule  single,  and  while  usually  aris- 
ing from  the  body  of  the  cell  may  be  given  off  from  one  of  the  larger 
protoplasmic  trunks.  Some  few  cells  have  more  than  one  axone,  and 
nerve  cells  without  axones  have  been  described.  In  Golgi  prepara- 
tions the  axone  is  distinguished  by  its  straighter  course,  more  uni- 
form diameter,  and  smoother  outline  (Fig.  61).  It  sends  off  few 
branches  (collaterals),  and  these  approximately  at  right  angles.  Both 
axone  and  collaterals  usually  end  in  terminal  arborizations .  In  most 
cells  the  axone  extends  a  long  distance  from  the  cell  body.  Such 
cells  are  known  as  Golgi  cell  type  I.  (Fig.  61).  In  others  the  axone 
branches  rapidly  and  ends  in  the  gray  matter  in  the  vicinity  of  its 
cell  of  origin — Golgi  cell  type  11.  (Fig.  62). 

As  they  leave  the  cell  body  the  neurofibrils  of  the  axone  converge 
to  a  very  narrow  portion  of  the  axone,  where  the  perifibrillar  sub- 
stance is  much  reduced  in  amount,  or  according  to  some,  entirely 
interrupted.  Beyond  this  the  fibrils  become  more  separated  and 
the  perifibrillar  substance  more  abundant. 

Some  axones  pass  from  their  cells  of  origin  to  their  terminations 
as  "naked"  axones,  i.e.,  uncovered  by  any  sheath.  Other  axones 
are  enclosed  by  a  thin  membrane,  the  neurilemma  or  sheath  of 
Schwann.  Still  others  are  surrounded  by  a  sheath  of  considerable 
thickness  known  as  the  medullary  sheath. 


NERVE    TISSUE. 


107 


Depending  upon  the  presence  or  absence  of  a  medullary  sheath, 
axones  may  thus  be  divided  into  two  main  groups — mcdullated  axones 
and  non-medullated  axones. 

1.  Nox-medullated  axones  (non-medullated  nerve  fibres)  (Fig. 
6j).  These  are  subdivided  into  non-medullated  axones  without  a 
neurilemma  and  non-medullated  axones  with  a  neurilemma. 

(a  Non-medullated  axones  without  a  neurilemma  are  merely  naked 
axones.      Present   in   large  numbers   in  the   embryo,  they  are  in  the 


h   >' 


d  -■—. 


—■d 


b  — 


B  A 

Fig.  63.  Fig.  64. 

FlG.  63.— Non-medullated  Nerve  Fibres  with  Neurilemma,  only  the  nuclei  of  which  can  be 

seen.  X  300. 
FlG.  64. — A,  Fresh  Medullated  Nerve  Fibre  from  Sciatic  Nerve  of  Guinea-pig'  (X  700I.  show- 
ing relative  size  of  axone  and  medullary  sheath.  B,  Medullated  Nerve  Fibre  from  Hu- 
man Cauda  Equina  (X  700)  (technic  4,  p.  113),  showing  shrunken  axone.  ii,  Axone  ;  b, 
medullary  sheath  ;  c,  node  of  Ranvier  ;  d,  neurilemma  ;  //,  incisures  of  Schmidt  ;  i,  nu- 
cleus of  neurilemma. 


adult  confined  to  the  gray  matter  and  to  the  beginnings  and  endings 
of  sheathed  axones,  all  of  the  latter  being  uncovered  for  a  short  dis- 
tance after  leaving  the  nerve  cell  body,  and  also  just  before  reaching 
their  terminations. 


ioS 


THE    TISSUES. 


k  _. 


—  d 


■:- 


(b)  Non-medullated  axones  with  a  neurilemma— fibres  of  Remafc. 
In  these  the  axone  is  surrounded  by  a  delicate  homogeneous,  nucleated 
sheath,  the  neurilemma  or  sheath  of  Schwann 
(Fig.  6$).  These  axones  are  described  by  some 
writers  as  having  no  true  neurilemma,  but  merely  a 
discontinuous  covering  of  flat  connective-tissue 
cells,  which  wrap  around  the  axone  and  corre- 
spond to  the  endoneurium  of  the  nerve  trunk 
.,     d     e  (see  page  339). 

I  2.  Medullated  axones  (med- 

ullated  nerve  fibres). — These,  like 
the  non-medullated,  are  subdivided 
according  to  the  presence  or  ab- 
sence of  a  neurilemma  into  med- 
ullated axones  with  a  neurilemma 
\  '  and  medullated  axones  without  a 
neurilemma. 

(a)  Medullated  axones  with  a 
neurilemma  constitute  the  bulk  of 
the  fibres  of  the  cerebro-spinal 
nerves..  Each  fibre  consists  of  (1) 
an  axone,  (2)  a  medullary  sheath, 
and  (3)  a  neurilemma. 

(1)  The  axone  is  composed  of 
neurofibrils  continuous  with  those 
of  the  cell  body,  and  like  them 
lying  in  a  perifibrillar  substance 
or  neuroplasm  (Fig.  65).  In  the 
fresh  condition  the  axone  is  broad, 
and  shows  faint  longitudinal  stri- 
ations  corresponding  to  the  neuro- 
fibrils, or  appears  homogeneous 
(Fig.  64,  A).  Fixatives  usually 
cause  the  axone  to  shrink  down 
to  a  thin  axial  thread,  whence  its 
older  name  of  axis-cylinder  (Fig. 
64,  B).  A  delicate  membrane  has 
been  described  by  some  as  enveloping  the  axone.  It  is  known  as 
the  axolemma  ox  periaxial  sheath  (Fig.  65). 


Fig.  65.  Fig.  66. 

FIG.  65.-  Diagram  of  Structure  of  a  Med- 
ullated Xerve  Fibre,  showing  two  differ- 
ent views  as  to  relations  of  neurilemma 
and  axilemma  and  their  behavior  at  the 
nodes  of  Ranvier.  rSzymonowicz.)  a, 
Neurofibrils;  b,  cement  substance;  r, 
axone  ;  d,  incisure  of  Schmidt  ;  e,  nucleus 
of  neurilemma  ;  /,  medullary  sheath  ;  g, 
sheath  of  Schwann  ;  //,  axone  ;  1,  axilem- 
ma ;  J,  sheath  of  Schwann;  k,  node  of 
Ranvier. 

FlG.  66— Piece  of  Medullated  Nerve  Fibre 
from  Human  Radial  Nerve.  X  400.  Os- 
mic-acid  fixation  and  stain.  (Szymono- 
wicz.)  a.  Medullary  sheath  ;  /<,  axone;  r, 
sheath  of  Henle  ;  d,  nuclei  of  Henle's 
sheath  ;  e,  nucleus  of  neurilemma. 


NERVE   TISSUE.  109 

(2)  The  medullary  sheath  (Figs.  64  and  65)  is  a  thick  sheath 
composed  of  a  semifluid  substance  resembling  fat  and  known  as  mye- 
lin. In  the  fresh  state  the  myelin  has  a  glistening  homogeneous 
appearance.  It  is  not  continuous,  but  is  divided  at  intervals  of  from 
80  to  600  '.i-  by  constrictions,  the  nodes  or  constrictions  of  Ranvier. 
That  portion  of  a  fibre  included  between  two  nodes  is  known  as  an 
intemode  (Fig.  65).  The  length  of  the  internode  is  usually  propor- 
tionate to  the  size  of  the  fibre,  the  smaller  fibres  having  the  shorter 
internodes.  In  fresh  specimens  the  medullary  sheath  of  an  inter- 
node is  continuous  (Fig.  64,  A),  but  in  fixed  specimens  it  appears 
broken  up  into  irregular  segments,  Schmidt-Lantermann  segments,  by 
clefts  which  pass  from  the  neurilemma  to  the  axolemma  or  axone, 
and  are  known  as  the  clefts  or  incisures  of  Schmidt-Lantermann  (Fig. 
64,  B).  On  boiling  medullated  nerve  fibres  in  alcohol  and  ether  a 
fine  network  is  brought  out  in  the  medullary  sheath,  the  neurokeratin 
network.  Owing  to  the  resistance  of  neurokeratin  to  the  action  of 
trypsin,  it  has  been  considered  as  possibly  similar  in  composition  to 
horn. 

(3)  The  neurilemma  or  sheath  of  Schwann  (Figs.  64,  B,  and  65)  is 
a  delicate  structureless  membrane  which  encloses  the  myelin.  At 
the  nodes  of  Ranvier  the  neurilemma  dips  into  the  constriction  and 
comes  in  contact  with  the  axone  or  axolemma.  Against  the  inner 
surface  of  the  neurilemma,  usually  about  midway  between  two  nodes, 
is  an  oval-shaped  nucleus,  the  nucleus  of  the  neurilemma  (Figs.  64,  B, 
and  66).  Each  nucleus  is  surrounded  by  an  area  of  granular  proto- 
plasm, and  makes  a  little  depression  in  the  myelin  and  a  slight  bulg- 
ing of  the  neurilemma  (Fig.  64,  B). 

In  addition  to  the  above-described  sheaths,  most  medullated  fibres 
of  peripheral  nerves  have,  outside  the  neurilemma,  a  nucleated  sheath 
of  connective-tissue  origin,  known  as  the  sheath  of  Henle  (Fig.  66). 

Two  views  as  to  the  relation  of  the  axolemma  to  the  neurilemma 
are  illustrated  in  Fig.  65.  According  to  one  the  neurilemma  is  con- 
tinuous, merely  dipping  into  the  nodes  of  Ranvier,  where  it  touches 
the  axolemma  or  the  axone.  According  to  the  second  both  neurilem- 
ma and  axolemma' are  interrupted  at  the  node,  but  unite  with  each 
other  there  to  enclose  completely  the  medullary  substance  of  the 
internode.      % 

Recent  experiments  of  Bethe  and  others  tend  to  prove  an  inter- 
ruption of  the  perifibrillar  substance  at  the  node  of  Ranvier.  They 
consider  the  axone  at  the  node  as  probably  crossed   by  a  sieve-like 


HO  THE    TISSUES. 

plate,  through  the  holes   of  which  the  fibrils   pass,  but  which   com- 
pletely interrupts  the  perifibrillar  substance. 

Medullated  nerve  fibres  vary  greatly  in  size.  The  finer  fibres 
have  a  diameter  of  from  2  to  4  /»,  those  of  medium  size  from  4  to 
10,'-',  the  largest  from  10  to  20,^.  They  have  few  branches,  and 
these  are  always  given  off  at  the  nodes  of  Ranvier. 

(b)  Medullated  axones  without  a  neurilemma  are  the  medullated 
nerve  fibres  which  form  the  white  matter  of  the  central  nervous  sys- 
tem. Their  structure  is  similar  to  the  above-described  structure  of 
a  medullated  nerve  fibre  with  a  neurilemma,  except  for  the  absence 
of  the  latter  sheath. 

As  to  the  physiological  significance  of  the  structural  elements  of 
the  neurone,  we  have  little  absolute  knowledge  but  certain  fairly  well- 
grounded  theories. 

That  portion  of  the  neurone  which  surrounds  the  nucleus — the 
cell  body — is,  as  already  stated,  the  genetic  or  birth  centre  of  the  neu- 
rone, the  nucleus  as  in  other  cells  being  probably  concerned  in  the 
general  cell  metabolism.  From  the  behavior  of  the  processes  when 
cut  off  from  the  cell  body  it  is  evident  that  the  latter  is  the  trophic 
or  nutritive  centre  of  the  neurone.  It  seems  probable  that  from  the 
standpoint  of  neurone  activity,  the  cell  body  usually  acts  as  the  func- 
tional centre  of  the  neurone,  the  processes  acting  mainly  as  channels 
through  which  impulses  are  received  and  distributed.  Certain  facts, 
such  for  example  as  the  entire  absence  of  chromophilic  bodies  in 
many  nerve  cells,  which  nevertheless  undoubtedly  functionate  ;  the  ab- 
sence of  these  bodies  in  all  axones;  the  diminution  of  the  chromatic 
substance  during  functional  activity;  its  much  greater  diminution  if 
activity  be  carried  to  the  point  of  exhaustion;  these  together  with 
its  behavior  under  certain  pathological  conditions  all  favor  the  theory 
that  the  stainable  substance  of  Nissl  is  not  the  active  nerve  element 
of  the  cell,  but  is  rather  of  the  nature  of  a  nutritive  element. 

There  thus  remain  to  be  considered  as  possible  factors  in  the 
transmission  of  the  nervous  impulse  the  neurofibrils  and  the  peri- 
fibrillar substance.  While  a  few  investigators  are  inclined  to  mag- 
nify the  importance  of  the  latter,  the  majority  agree  in  considering 
the  neurofibrils  as  the  actual  nervous  mechanism  of  the  neurone.  The 
already  referred  to  observations  of  Bethe  regarding  the  interruption 
of  the  perifibrillar  substance  at  the  constricted  portion  of  the  axone 
and  at  the  nodes  of  Ranvier,  thus  making  the  neurofibrils  the  only 
continuous  structure,  are  obviously  in  favor  of  this  view.  The 
neurofibrils  arc  probably  a  differentiation  of  the  spongioplasm,  while 
the  perifibrillar  substance  and  chromophilic  bodies  are  specializations 
of  the  hyaloplasm. 


NERVE   TISSUE.  i  i  i 

As  to  the  manner  in  which  neurones  are  connected,  there  are  two 
main  theories,  the  contact  theory  and  the  continuity  theory. 

According  to  the  contact  theory  each  neurone  is  a  distinct  and 
separate  entity.  Association  between  neurones  is  by  contact  or  con- 
tiguity of  the  terminals  of  the  axone  of  one  neurone  with  the  cell 
body  or  dendrites  of  another  neurone,  and  never  by  continuity  of  their 
protoplasm.  This  theory,  which  is  known  as  the  "neurone  theory" 
and  which  received  general  acceptance  as  a  result  of  the  work  of  Gol- 
gi,  His,  Forel,  Cajal,  and  others,  has  been  recently  called  in  question 
if  not  actually  disproved  by  the  discovery  of  the  continuity  of  the 
neurofibrils.  Based  upon  this  theory  is  the  so-called  "  retraction 
theory, "  which  held  that  a  neurone  being  associated  with  other  neu- 
rones only  by  contact  was  able  to  retract  its  terminals,  thus  breaking 
the  association  and  throwing  itself,  as  it  were,  out  of  circuit. 

According  to  the  more  recent  continuity  theory,  while  the  peri- 
fibrillar substance  is  interrupted  as  above  described,  the  neurofibrils 
are  continuous.  According  to  this  theory  the  neurofibrils,  which 
form  a  plexus  or  network  within  the  cell  body  and  dendrites,  are 
connected  with  a  pericellular  network — the  Golgi  net — which  closely 
invests  the  cell  body  and  its  dendrites.  Externally  the  Golgi  net 
is  further  connected  with  the  neurofibrils  of  the  axones  and  collate- 
rals of  other  nerve  cells.  This  connection  is  either  direct,  or,  as 
some  believe,  through  another  general  (diffuse)  extracellular  network. 
The  neurofibrils  are  thus,  according  to  this  theory,  continuous  and 
form  two  or  possibly  three  continuous  networks  :  (a)  an  intracellular 
network,  (b)  a  pericellular  network  (Golgi),  and  [c)  a  more  diffuse 
extracellluar  network,  lying  between  the  cells. 


Neuroglia. 

This  is  a  peculiar  form  of  connective  tissue  found  only  in  the 
central  nervous  system.  Unlike  the  other  connective  tissues,  neu- 
roglia is  of  ectodermic  origin,  being  developed  from  the  ectoder- 
mic  cells  which  line  the  embryonic  neural  canal.  These  cells,  at 
first  morphologically  identical,  soon  differentiate  into  neuroblasts  or 
future  neurones,  and  spongioblasts  or  future  neuroglia  cells.  In  the 
adult  two  main  types  of  neuroglia  cells  are  found — spider  cells  and 
mossy  cells  (Fig.  67).  Spider  cells  consist  of  a  central  portion  con- 
taining the  nucleus  and,  radiating  out  from  this,  delicate,  straight, 
un branched  processes.  Jllossy  cells  also  have  a  central  portion  con- 
taining the  nucleus,  from  which  pass  off  rough,  thick,  branching 
arms.  As  in  the  nerve  cell,  the  processes  of  neuroglia  cells  do  not 
anastomose,  but  form  a  network  of  interlacing  fibrils  for  the  support 


I  12 


THE    TISSUES. 


of  the  nervous  tissue  proper.  Spider  cells  occur  chiefly  in  the  white 
matter,  mossy  cells  in  the  gray  matter  in  connection  with  blood- 
vessels. While  these  represent  the  two  most  common  types  of  neu- 
roglia cells,  many  other  forms  occur,  which  are  probably  transitional 
between  the  two  types  described. 

According  to  Weigert,  what  are  in  Golgi  preparations  apparently 
processes  of  the  cells,  are  entirely  separate  neuroglia  fibres,  the  neu- 


FlG.  67.— A,  Mossy  Cell  from  Human  Cerebral  Cortex.     Golgi  method.     (Delafield  and  Prud- 
den.)     B,  Three  Spider  Cells  from  Cat's  Cerebral  Cortex.     (RetziusJ 


roglia  cells  having  no  processes.  Weigert  would  thus  make  the 
structure  of  neuroglia  analogous  to  that  of  fibrous  connective  tissue, 
i.e.,  composed  of  cells  and  a  fibrillar  intercellular  substance.  Other 
investigators  using  the  special  Weigert  neuroglia  stain  claim  that 
this  stain  fails  to  act  upon  the  non-fibrillar  elements  of  the  cell  body, 
and  that  the  apparently  separate  fibrils  are  really  a  part  of  the  proto- 
plasm of  the  neuroglia  cell. 

TECHNIC. 

(1)  Pieces  of  the  cerebral  cortex  are  stained  by  one  of  the  C.olgi  methods. 
If  the  rapid  or  mixed  silver  method  is  used,  sections  must  be  mounted  in  hard  bal- 
sam without  a  cover :  if  the  slow  silver  or  the  bichloride  method  is  used,  the  sections 
may  he  covered.  Sections  are  cut  from  75  to  100/'  in  thickness,  cleared  in  carbol- 
xylol  or  oil  ol  origanum  and  mounted  iii  balsam.  This  section  shows  only  the  ex- 
ternal morphology  of  the  neurone.  It  is  also  to  be  used  for  studying  the  different 
varieties  Oi  neuroglia  cells  as  demonstrated  by  Golgi's  method  (see  ])a,t;e  27). 


NERVE    TISSUE.  113 

(2)  Thin  transverse  slices  from  one  of  the  enlargements  of  the  spinal  cord 
are  fixed  in  absolute  alcohol.  Thin  sections  (5  to  10/-/)  are  stained  by  Nissl's 
method  (page  28)  and  mounted  in  balsam.  This  section  is  for  the  purpose  of 
studying  the  internal  structure  of  the  nerve  cell  and  processes  as  demonstrated  by 
the  method  of  Nissl. 

(3)  Medullated  Nerve  Fibres  (fresh). — Place  a  small  piece  of  one  of  the  sciatic 
or  lumbar  nerves  of  a  recently  killed  frog  in  a  drop  of  salt  solution  and  tease  longi- 
tudinally. Cover  and  examine  as  quickly  as  possible.  Note  the  diameter  of  the 
axone  and  of  the  medullary  sheath  and  the  appearance  of  the  nodes  of  Ranvier. 
An  occasional  neurilemma  nucleus  can  be  distinguished. 

(4)  Medullated  nerve  fibres — fibres  from  the  cauda  equina  (this  material  has 
the  advantage  of  being  comparatively  free  from  fibrous  connective  tissue)  are 
fixed  in  formalin-Muller's  fluid  (technic  5,  p.  5),  and  hardened  in  alcohol.  Small 
strands  are  stained  twenty  minutes  in  strong  picro-acid-fuchsin  solution  (technic  2, 
p.  16),  washed  thoroughly  in  strong  alcohol,  cleared  in  oil  of  origanum,  thoroughly 
teased  longitudinally  and  mounted  in  balsam. 

General  References  for  Further  Study  of  Tissues. 

Hertwig  :  Die  Zelle  und  die  Gewebe. 
Kolliker:  Handbuch  der  Gewebelehre. 
Ranvier:  Traite  Technique  d'Histologie. 

Cabot :  A  Guide  to  the  Clinical  Examination  of  the  Blood  for  Diagnostic  Pur- 
poses. 

Ewing :  Clinical  Pathology  of  the  Biood. 

Wood  :  Laboratory  Guide  to  Clinical  Pathology. 

Prenant,  Bouin  et  Maillard  :  Traite  d'Histologie. 

Barker:  The  Nervous  System. 

Van  Gehuchten  :   Le  Systeme  nerveux  de  l'homme. 

Bethe  :  Allgemeine  Anatomie  und  Physiologie  des  Nervensystem. 

8 


PART    IV. 
THE  ORGANS. 


CHAPTER    I. 

THE    CIRCULATORY    SYSTEM, 

The  circulatory  apparatus  consists  of  two  systems  of  tubular 
structures,  the  blood-vessel  system  and  the  lymph-vessel  system, 
which  serve  respectively  for  the  transmission  of  blood  and  lymph. 

THE   BLOOD-VESSEL   SYSTEM. 

This  consists  of  (a)  a  central  propelling  organ,  the  heart ;  (/>)  a 
series  of  efferent  tubules — the  arteries — which  by  branching  con- 
stantly increase  in  number  and  decrease  in  calibre,  and  which  serve 
to  carry  the  blood  from  the  heart  to  the  tissues  ;  (c)  minute  anasto- 
mosing tubules— the  capillaries — into  which  the  arteries  empty  and 
through  the  walls  of  which  the  interchange  of  elements  between  the 
blood  and  the  other  tissues  takes  place ;   {d)  a  system  of  converging 

tubules the  veins — which   receive  the  blood  from  the  capillaries, 

decrease  in  number  and  increase  in  size  as  they  approach  the  heart, 
and  serve  for  the  return  of  the  blood  to  that  organ. 

The  entire  system — heart,  arteries,  veins,  capillaries — has  a  com- 
mon and  continuous  lining,  which  consists  of  a  single  layer  of  endo- 
thelial cells.  Of  the  capillaries  this  single  layer  of  cells  forms  the 
only  wall.  In  the  heart,  arteries,  and  veins,  the  endothelium  serves 
simply  as  the  lining  for  walls  of  muscle  and  connective  tissue. 

Capillaries. 

It  is  convenient  to  describe  these  first  on  account  of  their  sim- 
plicity of  structure.  A  capillary  is  a  small  vessel  from  7  to  16//.  in 
diameter.  Its  wall  consists  of  a  single  layer  of  endothelial  cells. 
The  cells  are  somewhat  elongated  in  the  long  axis  of  the  vessel. 
Their  edges  are  serrated  and  are  united  by  a  small  amount  of  inter- 

117 


n8 


THE   ORGANS. 


cellular  substance.      Capillaries  branch  without  diminution  in  calibre, 
and  these  branches  anastomose  to  form  capillary  networks,  the  meshes 


FIG.  68.— Vein  and  Capillaries.     Silver-nitrate  and  hematoxylin  stain  (technic  7,  p.  62),  to  show- 
outlines  of  endothelial  cells  and  their  nuclei. 


fed 
FIG.  69.  -Diagram  of  Capillaries,  Small   Artery,  and  Vein,  showing  their  structure  and  rela- 
tions,    ti,  Capillaries  ;  b,  nuclei  of  capillary  endothelium  ;  c,  precapillary  arteries  ;  </,  arte- 
riole ;  e,  small  vein  ;    /,  small  artery. 

of  which  differ  in  size  and  shape  in  different  tissues  and  organs  (Figs. 
68,  69,  70). 

Arteries. 

The  wall  of  an  artery  consists  of  three  coats: 
fi  )   An  inner  coat,  the  intima. 
(2)   A  middle  coat,  the  media. 


THE   CIRCULATORY  SYSTEM. 


119 


(3)  An  outer  coat,  the  adventitia. 

The  intima  consists  of  a  single  layer  of  endothelial  cells,  con- 
tinuous with  and  similar  to  that  forming  the  walls  of  the  capillaries, 
or,  in  arteries  of  considerable  size,  of  this  layer  plus  more  or  less 
connective  tissue.  The  middle  coat  consists  mainly  of  smooth 
muscle,  the  outer  of  connective  tissue. 

The  structure  of  these  three  coats  varies  according  to  the  size  of 
the  artery,  and  while  the  transition  between  them  is  never  abrupt,  it 
is  convenient,  for  purposes  of  description,  to  distinguish  (a)  small 
arteries,  (b)  medium-sized  arteries,  and  (c)  large  arteries. 

Small  A  rteries. —  Passing  from  the  capillaries  back  along  an 
artery,  the  first  change  is  the  addition  of  a  thin  sheath  of  connective 
tissue  around  the  outside  of  the  endothelial  tube.  A  little  farther 
back  isolated  smooth  muscle  cells,  circularly  arranged,  begin  to  ap- 
pear between  the  endothelium  and  the  connective  tissue.  Such  an 
artery  is  known  as  a  precapillary  artery.     The  next  transition  is  the 


Fig.  70.— Capillary  Network  from  Human  Pia  Mater,  showing-  also  an  arteriole  in  "optical 
section  "  and  a  small  vein.  X  350.  (Technic  1,  p.  124.)  a,  Vein  ;  l\  arteriole  ;  c,  large  cap- 
illary ;  d,  small  capillaries. 


completion  of  the  muscular  coat,  the  muscle  cells  now  forming  a  con- 
tinuous layer.  Such  an  artery,  consisting  of  three  distinct  coats,  the 
middle  coat  composed  of  a  single  continuous  layer  of  smooth  muscle 
cells,  is  known  as  an  arteriole  (Fig.  69,  d ;   Fig.  70,  b). 

Medium-Sized  Arteries. — This   group  comprises  all    the   named 
arteries  of  the  body  with  the  exception  of  the  aorta  and  the  pulmo- 


120 


THE   ORGANS. 


nary.     Their  walls  are  formed  of  the  same  three  coats  found   in  the 
arteriole,  but  the  structure  of  these  coats  is  more  elaborate, 
i.  The  intima  consists  of  three  layers  (Fig.  71). 

(a)  An  inner  endothelial  layer  already  described. 

(b)  A  middle  layer,  the  intermediary  layer  of  the  intima.  This 
is  composed  of  delicate  white  and  elastic  fibrils  and  connective-tis- 
sue cells. 

(c)  An  outer  layer,  the  elastic  layer  of  the  intima,  or  membrana 
elastica  interna — a  thin  fenestrated  membrane  of  elastic  tissue.  This 
membrane  is  intimately  connected  with  the  media  and  marks  the 


FIG.  71. — From  Cross-section  through  Walls  of  Medium-sized  Artery  and  its  Accompanying- 
Vein.  X  75.  (Technic  3,  p.  125.)  A,  Tntima  of  artery;  a,  its  endothelial  layer  ;  b,  its  in- 
termediary layer  ;  c,  its  elastic  layer  ;  B,  media  of  artery  ;  C,  adventitia,  the  upper  part 
belonging  to  the  artery,  the  lower  to  the  vein  ;  within  the  adventitia  are  seen  the  vasa 
vasorum  ■  D,  media  of  vein  ;  H,  intima  of  vein  ;  r,  its  intermediary  layer  ;  /,  its  endothe- 
lial layer. 

boundary  between  the  latter  and  the  intima.  In  the  smallest  of  the 
medium-sized  arteries  the  intermediary  layer  is  often  wanting,  the 
endothelial  cells  resting  directly  upon  the  elastic  membrane.  Owing 
to  the  extensive  amount  of  elastic  tissue  in  their  walls,  there  is  a 
post-mortem  contraction  of  arteries  which  results  in  the  intima  being 
thrown  up  into  folds.  For  this  reason  the  elastic  membrane  pre- 
sents, in  transverse  sections  of  an  artery,  the  appearance  of  a  wavy 
band  (Fig.   71). 


THE   CIRCULATORY  SYSTEM.  121 

2.  The  media  is  a  thick  coat  of  circularly  disposed  smooth  mus- 
cle cells  (Fig.  71).  Its  thickness  depends  largely  upon  the  size  of 
the  vessel,  though  varying  somewhat  for  different  vessels  of  the 
same  size.  A  small  amount  of  fibrillar  connective  tissue  supports 
the  muscle  cells.  Elastic  tissue  is  present  in  the  media,  the  amount 
being  usually  proportionate  to  the  size  of  the  vessel.1  In  the  smaller 
of  the  medium-sized  arteries,  the  elastic  tissue  is  disposed  as  delicate 
fibrils  among  the  muscle  cells.  In  larger  arteries  many  coarse  fibres 
are  intermingled  with  the  fine  fibrils.  When  much  elastic  tissue  is 
present  the  muscle  cells  are  separated  into  more  or  less  well-defined 
groups.  In  such  large  arteries  as  the  subclavian  and  the  carotid, 
elastic  tissue  occurs  not  only  as  fibrils  but  also  as  circularly  disposed 
plates  or  fenestrated  membranes. 

3.  The  adventitia  (Fig.  71)  is  composed  of  loose  fibrous  connec- 
tive tissue  with  some  elastic  fibres.  Occasionally  there  are  scattered 
smooth  muscle  cells.  Both  smooth  muscle  cells  and  elastic  fibres  are 
arranged  longitudinally.  The  adventitia  does  not  form  a  definitely 
outlined  coat  like  the  media  or  intima,  but  blends  externally  with  the 
tissues  surrounding  the  artery  and  serves  to  attach  the  artery  to  these 
tissues.  In  some  of  the  larger  arteries  the  elastic  tissue  of  the  ad- 
ventitia forms  an  especially  well-defined  layer  at  the  outer  margin 
of  the  media.  This  is  known  as  the  menibrana  elastica  externa.  In 
general  it  may  be  said  that  the  thickness  of  the  adventitia  and  the 
amount  of  elastic  tissue  present  are  directly  proportionate  to  the  size 
of  the  artery. 

Large  arteries  like  the  aorta  (Fig.  72)  have  the  same  three  coats 
as  small  and  medium-sized  arteries.  The  layers  are  not,  however,  so 
distinct.  This  is  due  mainly  to  the  excessive  amount  of  elastic  tis- 
sue in  the  media  (Fig.  73),  which  makes  indistinct  the  boundaries 
between  intima  and  media,  and  between  media  and  adventitia.  The 
walls  of  the  aorta  are  thin  in  proportion  to  the  size  of  the  vessel,  in- 
creased strength  being  obtained  by  the  decided  increase  in  the 
amount  of  elastic  tissue.      Of  the  intima,  the  endothelial  cells  are 

1  This  proportion  does  not  obtain  for  all  vessels.  Thus  in  the  radial,  femoral, 
and  coeliac  arteries  there  is  comparatively  little  elastic  tissue,  while  in  the  common 
iliac,  carotid,  and  axillary  the  elastic  tissue  is  in  excess  of  the  muscular. 

The  disposition  of  elastic  tissue  in  the  walls  of  arteries  which  supply  the  brain 
is  somewhat  peculiar.  The  inner  elastic  membrane  is  especially  well  denned. 
There  are  but  few  elastic  elements  in  the  media,  and  the  longitudinally  disposed 
fibres  of  the  adventitia  are  almost  entirely  wanting. 


122  THE  ORGANS. 

short  and  polygonal ;  the  intermediary  layer  similar  to  that  of  a  me- 
dium-sized artery;  the  elastic  layer  less  distinct  and  often  broken  up 
into  several  thin  layers.     The  media  consists  mainly  of  elastic  tissue 


IV 


FIG.  72.  — From  Transverse  Section  of  Dog's  Aorta.     X  60.     (Technic  4,  p.  125.)     </,  Intima;^, 
media  ;  c,  adventitia  ;  d,  vasa  vasorum  ;  e,  elastic  tissue  ;  f,  endothelium. 

arranged  in  circular  plates  or  fenestrated  membranes.  Between  the 
elastic-tissue  plates  are  groups  of  smooth  muscle  cells  and  some 
fibrillated  connective  tissue.  The  adventitia  resembles  that  of  the 
medium-sized  artery.      There  is  no  external  elastic  membrane. 

Veins. 

The  walls  of  veins  resemble  those  of  arteries.  There  are  the 
same  three  coats,  iutivia,  media,  and  adventitia,  and  the  same  ele- 
ments enter  into  the  structure  of  each  coat  (Fig.  71).  Venous  walls 
arc  not,  however,  so  thick  as  those  of  arteries  of  the  same  calibre,  and 
the  coats  are  not  so  distinctly  differentiated  from  one  another.  The 
transition  from   capillary  through  the  precapillary  vein  to  the  small 


THE   CIRCULATORY  SYSTEM. 


123 


vein  is  similar  to  that  described  under  arteries  (page  119).  Unlike 
the  artery,  the  thickness  of  the  wall  of  a  vein  and  its  structure  are  not 
directly  proportionate  to  the  size  of  the  vessel,  but  depend  also  upon 
other  factors  such  as  the  position  of  the  vein  and  the  support  given 
to  its  walls  by  surrounding  structures. 

Of  the  intima  the  endothelial  layer  and  the  intermediary  layer 
are  similar  to  those  of  the  artery.  The  elastic  layer  is  not  always 
present,  is  never  so  distinct,  and  is  not  wavy  as  in  the  artery  (Fig. 
71).  The  result  is  a  lack  of  demarcation  between  intima  and  media, 
the  connective  tissue  of  the  intermediary  layer  of  the  intima  merging 
with  the  mixed  muscle  and  connective  tissue  of  the  media.  Project- 
ing at  intervals  from  the  inner  surface  of  the  wall  of  most  veins  are 


Fir,.  73. — From  Transverse  Section  of  Dog's  Aorta,  to  show  Elastic  Tissue.    X  60.     (Technic  7, 
p.  125.)     Elastic  tissue  stained  black,     a.  Intima  ;  b,  media  ;  c,  adventitia. 


valves.     These  are  derived  entirely  from  intima  and  consist  of  loose 
fibrous  and  elastic  tissue  covered  by  a  single  layer  of  endothelium. 

The  media  of  veins  is  thin  as  compared  with  that  of  arteries  of 
the  same  size.      It  consists  of  fibrous  and  elastic  tissue  and  smooth 


124  THE   ORGANS. 

muscle  cells.     The  amount  of  muscle  is  comparatively  small  and  the 
cells  are  arranged  in  groups  through  the  connective  tissue. 

The  adventitia  is  well  developed  in  proportion  to  the  media. 
It  consists  of  mixed  fibrous  and  elastic  tissue  and  usually  contains 
along  its  inner  margin  small  bundles  of  longitudinally  disposed 
smooth  muscle  cells. 

The  media  is  thickest  in  the  veins  of  the  lower  extremities  and 
in  the  veins  of  the  skin.  In  the  veins  of  the  head  and  abdomen  the 
media  is  very  thin,  while  in  the  subclavian  and  superior  vena  cava 
and  in  the  veins  of  bones,  of  the  pia  mater,  dura  mater,  and  retina, 
there  is  an  almost  entire  absence  of  media. 

Arteries  are  as  a  rule  empty  after  death,  while  veins  contain  blood. 
The  absence  of  much  elastic  tissue  in  the  walls  of  the  veins  prevents 
any  such  extensive  post-mortem  contraction  as  occurs  in  the  arteries. 
Veins  tend  to  collapse  after  death,  but  are  usually  prevented  from 
doing  so  by  the  presence  of  blood  in  them. 

Vasa  Vasorum. — Medium  and  large  arteries  and  veins  are  sup- 
plied with  small  nutrient  vessels — vasa  vasorum.  These  vessels  run 
in  the  adventitia,  small  branches  penetrating  the  media  (Figs,  yi 
and  72). 

Lymph  channels  are  found  on  the  outer  surface  of  many  blood-ves 
sels.      Some  of  the  smaller  vessels  are  surrounded  by  spaces  lined  by 
endothelium — perivascular  lyrnpJi  spaces.     These  communicate  with 
the  general  lymphatic  system. 

Nerves. — The  walls  of  the  blood-vessels  are  supplied  with  both 
medullated  and  non-medullated  fibres.  The  latter  are  axones  of 
sympathetic  neurones.  As  these  nerves  control  the  calibre  of  the 
vessels  they  are  known  as  vasomotor  nerves.  They  form  plexuses 
in  the  adventitia,  from  which  are  given  off  branches  which  penetrate 
the  media  and  terminate  on  the  muscle  cells  (page  350).  The  medul- 
lated fibres  are  the  peripheral  arms  of  spinal  or  cranial  ganglion  cells. 
The  larger  fibres  run  in  the  connective  tissue  outside  the  adventitia. 
From  these  are  given  off  branches  which  enter  the  media,  divide 
repeatedly,  lose  their  medullary  sheaths,  and  terminate  mainly  in  the 
media,  although  some  fibres  have  been  traced  to  their  terminations 

in  the  intima. 

TECHNIC. 

( i)  Capillaries,  Arterioles,  Small  Arteries,  and  Veins.— Fix  an  entire  brain,  or 
slices  about  an  inch  thick  from  its  surface,  in  formalin-Midler's  fluid  for  twenty- 
four  hours  (technic  5,  p.  5).     Remove  the  pia  mater,  especially  the  thinner  parts 


THE   CIRCULATORY  SYSTEM.  125 

which  lie  in  the  sulci  between  the  convolutions,  and  harden  in  graded  alcohols. 
Select  a  thin  piece,  stain  with  hematoxylin  (lightly)  and  eosin  (strongly),  (technic 
1,  p.  16),  and  mount  in  balsam  or  in  eosin-glycerin.  The  veins,  having  thin  walls 
and  being  usually  well  filled  with  blood,  appear  distinct  and  red  from  the  eosin- 
stained  red  cells.  The  arteries,  having  thicker  walls,  in  which  are  many  haemo- 
globin-stained nuclei,  have  a  rather  purple  color.  Between  the  larger  vessels  can 
be  seen  a  network  of  anastomosing  capillaries  with  their  thin  walls  and  bulging 
nuclei.  Some  are  filled  with  blood  cells ;  others  are  empty  with  their  collapsed 
walls  in  apposition.  Note  the  appearance  of  an  arteriole,  first  focussing  on  its 
upper  surface,  then  focussing  down  through  the  vessel.  In  this  way  what  is  known 
as  an  "optical  section"  is  obtained,  the  artery  appearing  as  if  cut  longitudinally. 
Trace  the  transition  from  arteriole  to  precapillary  artery  and  the  breaking  up  of 
the  latter  into  the  capillary  network.  Similarly  follow  the  convergence  of  capil- 
laries to  form  a  small  vein. 

(2)  Instructive  pictures  of  the  relations  of  arteries,  capillaries,  and  veins  in  liv- 
ing tissues  may  be  obtained  by  curarizing  a  frog,  distending  the  bladder  with  nor- 
mal saline  introduced  through  a  small  catheter  or  cannula,  opening  the  abdomen 
and  drawing  out  the  bladder,  which  can  then  be  arranged  upon  the  stage  of  the 
microscope.  The  passage  of  the  blood  from  the  arteries  through  the  capillary  net- 
work and  into  the  veins  is  beautifully  demonstrated. 

(3)  For  studying  the  structure  of  the  walls  of  a  medium-sized  artery  and  vein 
remove  a  portion  of  the  radial  artery,  or  other  artery  of  similar  size,  and  its  accom- 
panying vein,  together  with  some  of  the  surrounding  tissues.  Suspend  the  vessels, 
with  a  small  weight  attached,  in  formalin-M filler's  fluid  (technic  5,  p.  5).  Sec- 
tions should  be  cut  transversely,  stained  with  haematoxylin-eosin  (technic  1,  p.  16), 
or  with  haematoxylin-picro-acid  fuchsin  (technic  3,  p.  16),  and  mounted  in  balsam. 
The  vessels  of  the  adventitia  — vasa  vasorum  — are  convenient  for  studying  the 
structure  of  arterioles  and  small  veins. 

(4)  Fix  a  piece  of  aorta  in  formalin-M filler's  fluid,  care  being  taken  not  to 
touch  the  delicate  endothelial  lining.  Stain  transverse  sections  with  haematoxylin- 
eosin  or  with  haematoxylin-picro-acid  fuchsin  and  mount  in  balsam. 

(5)  The  outlines  of  the  lining  endothelial  cells  may  be  demonstrated  as  follows  : 
Kill  a  small  animal,  cut  the  aorta,  insert  a  glass  cannula  and,  under  low  pressure, 
thoroughly  wash  out  the  entire  vascular  system  with  distilled  water.  Follow  the 
water  by  a  one-per-cent  aqueous  solution  of  silver  nitrate.  Remove  some  of  the 
smaller  vessels,  split  longitudinally,  mount  in  glycerin,  and  expose  to  the  direct 
sunlight.  After  the  specimen  has  turned  brown  examine  with  the  low  power.  The 
outlines  of  the  cells  should  appear  brown  or  black. 

(6)  The  endothelium  of  the  smaller  vessels  and  capillaries  may  also  be  demon- 
strated in  the  specimen,  described  under  technic  8,  p.  62. 

(7)  The  elastic  tissue  of  the  blood-vessels  is  best  demonstrated  by  means  of 
Weigert's  elastic  tissue  stain.  Prepare  sections  of  medium-sized  vessels  and  of 
the  aorta,  as  above  described  (3),  and  stain  as  in  technic  3,  p.  23. 


The   Heart. 

The  heart  is  a  part  of  the  blood-vessel  system  especially  differ 
entiated  for  the  purpose  of  propelling  the  blood  through  the  vessels. 
The  main  mass  of  the  heart  wall  consists  of  a  special  form  of 


126  THE   ORGANS. 

muscle  tissue  already  described  as  heart  muscle  (page  96).  This 
constitutes  the  myocardium.  On  its  inner  and  outer  sides  the  myo- 
cardium is  covered  by  connective-tissue  membranes  lined  respectively 
with  endothelium  and  mesothelium  and  known  as  the  endocardium 
and  cpicardium. 

The  myocardium  varies  in  thickness  in  different  parts  of  the 
heart,  being  thickest  in  the  left  ventricle,  thinnest  in  the  auricles. 
A  ring  of  dense  connective  tissue,  the  auriculo-ventricular  ring,  com- 
pletely separates  the  muscle  of  the  auricles  from  that  of  the  ven- 
tricles. The  auricular  muscle  consists  of  an  outer  coat  common  to 
both  auricles,  the  fibres  of  which  have  a  transverse  direction,  and  of 
an  inner  coat,  independent  for  each  auricle,  the  fibres  of  which  are 
longitudinally  disposed.  Between  the  two  coats  bundles  of  muscle 
fibres  are  frequently  found  which  run  in  various  directions. 

The  disposition  of  the  muscle  tissue  of  the  ventricles  is  much 
more  complicated.  It  is  usually  described  as  composed  of  several 
layers,  the  fibres  of  which  run  in  different  directions.  The  meaning 
of  these  fibre  layers  becomes  apparent  when  we  study  the  arrange- 
ment of  the  fibres  in  embryonic  hearts  in  which  the  connective  tissue 
has  been  broken  down  by  maceration.  Thus  dissected,  the  muscle  of 
the  ventricles  is  seen  to  consist  mainly  of  two  set  of  fibres,  a  super- 
ficial set  and  a  deep  set.  These  run  at  right  angles  to  each  other. 
Both  sets  of  fibres  begin  at  the  auriculo-ventricular  rings.  The 
superficial  fibres  wind  around  both  ventricles  in  a  spiral  manner,  be- 
coming constantly  deeper,  to  terminate  in  the  papillary  muscles  of  the 
opposite  ventricle.  The  deeper  fibres  pass  from  the  auriculo-ven- 
tricular ring  around  the  ventricle  of  the  same  side,  through  the  inter- 
ventricular septum  and  terminate  in  the  papillary  muscles  of  the 
opposite  ventricle. 

The  endocardium  covers  the  inner  surface  of  the  myocardium 
and  forms  the  serous  lining  of  all  the  chambers  of  the  heart.  At  the 
arterial  and  venous  orifices  it  is  seen  to  be  continuous  with  and  simi- 
lar in  structure  to  the  intima  of  the  vessels.  It  consists  of  two  lay- 
ers :  (a)  an  inner  composed  of  a  single  layer  of  endothelial  cells,  cor- 
responding to  the  endothelial  lining  of  the  blood-vessels;  and  (/>) 
an  outer  composed  of  mixed  fibrous  and  elastic  tissue  and  smooth 
muscle  cells.  Externally  the  endocardium  is  closely  attached  to  the 
myocardium. 

Strong  fibrous  rings  (annuli  fibrosi),  composed   of  mixed  fibrous 


THE   CIRCULATORY  SYSTEM.  12/ 

and  elastic  tissue,  surround  the  openings  between  auricles  and  ven- 
tricles. Similar  but  more  delicate  rings  encircle  the  openings  from 
the  heart  into  the  blood-vessels. 

The  Jieart  valves  are  attached  at  their  bases  to  the  annuli  fibrosi. 
They  are  folds  of  the  endocardium,  and  like  the  latter  consist  of 
fibrous  and  elastic  tissue  continuous  with  that  of  the  rings  and  cov- 
ered by  a  layer  of  endothelium. 

The  epicardium  is  the  visceral  layer  of  the  pericardium.  It  is  a 
serous  membrane  like  the  endocardium,  which  it  resembles  in  struc- 
ture. It  consists  of  a  layer  of  mixed  fibrous  and  elastic  tissue  cov- 
ered over  by  a  single  layer  of  mesothelial  cells.  Beneath  the  epicar- 
dium there  is  usually  more  or  less  fat. 

Blood-vessels. — Blood  for  the  nutrition  of  the  heart  is  supplied 
through  the  coronary  arteries.  The  larger  branches  run  in  the  con- 
nective tissue  which  separates  the  bundles  of  muscle  fibres.  From 
these,  smaller  branches  pass  in  among  the  individual  fibres,  where 
they  break  up  into  a  rich  capillary  network  with  elongated  meshes. 
From  the  myocardium,  capillaries  penetrate  the  connective  tissue  of 
the  epicardium  and  endocardium.  The  auriculo-ventricular  valves 
are  supplied  with  blood-vessels,  while  in  the  semilunar  valves  blood- 
vessels are  wanting. 

Lymphatics. — Lymph  channels  traverse  the  epicardium  and  endo- 
cardium and  enter  the  valves.  Within  the  myocardium  minute 
lymph  vessels  have  been  demonstrated  between  the  muscle  fibres  and 
accompanying  the  blood-vessels. 

Nerves. — These  are  derived  from  both  cerebro-spinal  and  sym- 
pathetic systems,  and  consist  of  both  medullated  and  non-medullated 
fibres.  Sympathetic  ganglion  cells  are  distributed  in  groups  through- 
out the  myocardium.  Among  these  cells  the  nerve  fibres  form  plex- 
uses from  which  both  motor  and  sensory  terminals  are  given  off  to 
the  muscle.     (For  nerve  endings  in  heart  muscle  see  page  350.) 

TECHNIC. 

(1)  The  Heart. — Cut  pieces  through  the  entire  thickness  of  the  wall  of  one  of 
the  ventricles,  care  being  taken  not  to  touch  either  the  serous  surface  or  the  lining 
endothelium.  Fix  in  formalin-M tiller's  fluid  (technic  5.  p.  5).  Cut  transverse 
and  longitudinal  sections;  stain  with  haematoxylm-eosin  (technic  1.  p.  16)  and 
mount  in  balsam. 

(2)  Treat  the  entire  heart  of  a  small  animal  {e.g..  guinea-pig  or  frog)  in  the 
same  manner  as  the  preceding,  making  transverse  sections  through  both  ventricles. 

(3)  An  entire  heart,  human  or  animal,  may  be  fixed  in  the  distended  condition 


128  THE   ORGANS. 

by  filling  with  formalin-Miiller's  fluid  under  low  pressure  and  then  tying  off  the 
vessels.  The  entire  heart  thus  distended  is  placed  in  a  large  quantity  of  the  same 
fixative. 

Development  of  the  Circulatory  System. 

The  blood-vessels  and  the  heart  begin  their  development  sepa- 
rately and  afterward  become  united.  Both  are  derived  from  meso- 
derm. The  earliest  vessels  to  be  formed  are  the  capillaries.  These 
make  their  appearance  in  the  mesodermic  tissue  near  the  periphery 
of  the  area  vasculosa  which  surrounds  the  developing  embryo.  Here 
groups  of  cells  known  as  "blood  islands  "  differentiate  from  the  rest 
of  the  mesodermic  cells.  Within  these  islands  channels  appear 
which  are  lined  with  flat  cells  derived  from  cells  of  the  islands. 
These  represent  the  earliest  capillaries.  In  post-embryonic  life 
new  capillaries  develop  by  outgrowths  from  already  existing  capil- 
laries. These  capillary  "  buds,"  at  first  solid,  push  their  way 
through  the  intervening  tissue  and  unite  with  similar  buds  from 
other  capillaries.  Through  this  solid  structure  a  lumen  is  hollowed 
out  by  extension  of  the  lumina  of  the  older  capillaries.  Arteries 
and  veins  are  developed  from  the  capillaries  by  a  further  differen- 
tiation of  the  surrounding  mesodermic  cells  to  form  the  muscular 
and  connective-tissue  coats  outside  the  first-formed  capillary  tube. 

The  heart  and  the  roots  of  the  large  vessels  which  spring  from  it, 
while  also  of  mesoblastic  origin,  have  an  entirely  different  early 
development.  The  heart  first  appears  as  an  endothelial  tnbe,  which 
develops  like  the  capillaries  by  differentiation  of  mesodermic  cells. 
Other  mesodermic  cells  next  form  an  entirely  separate  muscular  tube 
around  the  endothelial  tube.  This  is  the  primitive  myocardium. 
These  two  tubes  are  at  first  united  only  in  places  by  bands  of  con- 
nective tissue.  Later  they  approach  each  other  so  that  the  inner 
tube,  the  endocardium,  becomes  a  lining  for  the  outer  tube,  the  myo- 
cardium. The  epicardium,  as  the  visceral  layer  of  the  pericardium, 
has  a  separate  origin,  being  constricted  off  from  that  portion  of  the 
mesoderm  which  lines  the  primary  body  cavity. 

The  Lymph-Vessel  System. 

The  larger  lymph  vessels  are  similar  in  structure  to  veins.  Their 
walls  are,  however,  thinner  than  those  of  veins  of  the  same  calibre 
and  they  contain  more  valves.  They  are  capable  of  great  distention, 
and  when  empty  collapse  so  that  their  thin  walls  are  in  apposition. 


THE   CIRCULATORY  SYSTEM.  129 

The  largest  of  the  lymph  vessels,  the  thoracic  duct,  has  three  well- 
defined  coats  :  an  intima  consisting  of  the  usual  lining  endothelium 
resting  upon  a  subendothelial  layer  of  delicate  fibro-elastic  tissue,  the 
outermost  elastic  fibres  having  a  longitudinal  arrangement ;  a  fairly 
thick  media  of  circularly  disposed  smooth  muscle  cells ;  and  an  ad- 
ventitia  which  is  strengthened  by  bundles  of  longitudinal  smooth 
muscle. 

Lymph  capillaries  resemble  blood  capillaries  in  that  their  walls 
are  composed  of  a  single  layer  of  endothelial  cells.  The  cells  are 
rather  larger  and  more  irregular  than  in  blood  capillaries,  the  capil- 
laries themselves  are  larger,  and,  instead  of  being  of  uniform  diameter 
throughout,  vary  greatly  in  calibre  within  short  distances.  In  cer- 
tain tissues  dense  networks  of  these  lymph  capillaries  are  found. 
Cleft-like  lymph  spaces — perivascular  lymph  spaces — partially  sur- 
round the  walls  of  the  smaller  blood-vessels. 

Lymph  spaces  without  endothelial  or  other  apparent  lining  also 
occur.  Examples  of  these  are  the  pericellular  lymph  spaces  found  in 
various  tissues  and  the  canalicnli  of  the  cornea  and  of  bone  (pages 
64  and  83). 

Similar  in  character  to  lymph  spaces  are  the  body  cavities,  peri- 
toneal, pleural,  and  pericardial,  with  their  linings  of  serous  membranes. 
These  cavities  first  appear  in  the  embryo  as  a  cleft  in  the  mesoderm 
— the  cxlom,  body  cavity,  or  plcnroperitoneal  cleft.  This  cleft  is 
lined  with  mesothelium  beneath  which  the  stroma  is  formed.  These 
membranes  not  only  line  the  cavities,  but  are  reflected  over  most  of 
the  viscera  of  the  abdomen  and  thorax.  They  consist  of  a  stroma  of 
mixed  fibrous  and  elastic  tissue,  covered  on  its  inner  side  by  a  layer 
of  mesothelium,  the  two  being  separated  by  a  homogeneous  basement 
membrane.  The  stroma  contains  numerous  lymphatics.  These 
communicate  with  the  free  surfaces  by  means  of  openings — stomata 
— surrounded  by  cuboidal  cells,  whose  shape  and  granular  protoplasm 
distinguish  them  from  the  neighboring  flat  mesothelium. 

TECHNIC. 

(1)  Remove  a  portion  of  the  central  tendon  of  a  rabbit's  diaphragm.  Rub 
the  pleural  surface  gently  with  the  finger  or  with  a  brush  to  remove  the  mesothe- 
lium. Rinse  in  distilled  water  and  treat  with  silver  nitrate  as  in  technic  7,  p.  62. 
Mount  in  glycerin.  If  the  silver  impregnation  is  successful,  the  networks  of 
coarser  and  finer  lymphatics  can  be  seen  as  well  as  the  outlines  of  the  endothelium 
of  their  walls.  If  care  has  been  taken  not  to  touch  the  peritoneal  surface,  the 
peritoneal  mesothelium  and  the  stomata  are  frequently  seen. 
9 


130  THE   ORGANS. 

(2)  The  Thoracic  Duct. — Remove  a  portion  of  the  thoracic  duct,  fix  in  for- 
malm-Miiller's  fluid  (technic  5.  p.  5),  and  stain  sections  with  haematoxylin-eosin 
(technic  1.  p.  16). 

The  Carotid  Gland. 

This  is  a  small  ductless  gland  which  lies  at  the  bifurcation  of  the 
carotid  artery.  It  is  composed  of  a  vascular  connective  tissue  sup- 
porting spheroidal  groups  of  polyhedral  epithelial  cells  which  are 
closely  associated  with  tufts  of  capillaries.  Some  of  the  gland  cells 
take  a  brownish  stain  with  chromic  acid  similar  to  the  medullary 
cells  of  the  adrenal. 

The  Coccygeal  Gland. 

This  is  also  a  ductless  gland  similar  in  structure  to  the  preceding, 
but  with  much  more  irregularly  arranged  groups  of  cells. 

TECHNIC. 
Technic  same  as  for  Thyroid  Gland,  page  253. 

General  References  for  Further  Study  of  the  Circulatory  System. 

Kolliker:   Handbuch  der  Gewebelehre  des  Menschen,  vol.  iii. 
Stohr:  Text-book  of  Histology. 

Schafer:  Histology  and  Microscopic  Anatomy,  in  Quain's  Elements  of  Anat- 
omv.  tenth  edition. 


CHAPTER    II. 

LYMPHATIC    ORGANS. 

The    Lymph    Nodes. 

Lymph  nodes  are  small  bodies,  usually  oval  or  bean-shaped,  which 
are  distributed  along  the  course  of  the  lymph  vessels.  In  some 
regions  they  are  arranged  in  series  forming  "  chains  "  of  lymph  nodes 
as,  e.g.,  the  axillary  and  inguinal. 

Each  lymph  node  is  surrounded  by  a  capsule  of  connective  tissue 
which   sends  trabecules  or  septa  into   the   organ.      The   capsule   and 


*  8  f 

FIG.  74. — Section  through  Entire  Human  Lymph  Node,  including-  Hilum.  X  15.  (Technic  1, 
p.  134.)  Dark  zone,  cortex  ;  light  central  area,  medulla,  a,  Lymph  nodule  of  cortex  ;  />, 
germinal  centres;  c,  trabeculae  containing  blood-vessels;  d,  capsule;  e.  hilum  ;  f\  lvmph 
sinus  of  medulla  ;  g,  lymph  cords  of  medulla  ;  //,  lymph  sinuses  of  medulla  and  cortex. 


septa  constitute  the    connective-tissue  frameivork  of  the  node,   and 
serve  as  a  support  for  the  lymphatic  tissue  (Fig.  74). 

The  capsule  is  composed  of  fibrous  connective  tissue  arranged  in 
two  layers.     In  the  outer  the  fibres  are  loosely  arranged  and  serve, 

131 


132  THE   ORGANS. 

like  the  fibres  of  the  arterial  adventitia,  to  attach  the  node  to  the 
surrounding  tissues.  The  inner  layer  of  the  capsule  consists  of  a 
more  dense  connective  tissue  and  contains  some  smooth  muscle  cells. 
At  one  point,  known  as  the  hilum  (Fig.  74),  there  is  a  depression 
where  the  connective  tissue  of  the  capsule  extends  deep  into  the  sub- 
stance of  the  node.  This  serves  as  the  point  of  entrance  for  the 
main  arteries  and  nerves,  and  of  exit  for  the  veins  and  efferent  lymph 
vessels. 

The  connective-tissue  septa,  which  extend  from  the  capsule  into 
the  interior  of  the  node,  divide  it  into  irregular  intercommunicating 
compartments.  In  the  peripheral  portion  of  the  node  these  compart- 
ments are  somewhat  spheroidal  or  pear-shaped.  Toward  the  centre 
of  the  node  the  septa  branch  and  anastomose  freely,  with  the  result 
that  the  compartments  are  here  narrower,  more  irregular,  and  less 
well  defined.  This  arrangement  of  the  connective  tissue  allows  the 
division  of  the  node  into  two  parts,  an  outer  peripheral  part  or  cortex 
and  a  central  portion,  the  medulla  (Fig.  74). 

Within  the  compartments  formed  by  the  capsule  and  the  septa  is 
the  lymphatic  tissue  (for  structure  see  page  75).  In  the  cortex 
where  the  compartments  are  large  and  spheroidal  or  pear-shaped,  the 
lymphatic  tissue  is  of  the  compact  variety,  and  is  arranged  in  masses 
which  correspond  in  shape  to  the  compartments.  These  are  known 
as  lymph  nodules  (Fig.  74).  In  the  centre  of  each  n6dule  is  usually 
an  area  in  which  the  cells  are  larger,  are  not  so  closely  packed,  and 
show  marked  mitosis.  As  it  is  here  that  active  proliferation  of  lym- 
phoid cells  takes  place,  this  area  is  known  as  the  germinal  centre 
(Figs.  74  and  75).  Immediately  surrounding  the  germinal  centre  is 
a  zone  in  which  the  lymphoid  cells  are  more  closely  packed  than  else- 
where in  the  nodule  (Fig.  75).  This  is  apparently  due  to  the  active 
production  of  new  cells  at  the  germinal  centre  and  the  consequent 
pushing  outward  of  the  surrounding  cells.  In  stained  sections  the 
centre  of  the  nodule  is  thus  lightly  stained,  while  immediately  sur- 
rounding this  light  area  is  the  darkest  portion  of  the  nodule  (Fig. 
75).  From  the  inner  sides  of  the  nodules  strands  of  lymphoid  tissue 
extend  into  the  medulla.  These  are  known  as  lymph  cords,  and  anas- 
tomose freely  in  the  small  irregular  compartments  of  the  medulla. 
In  both  cortex  and  medulla  the  lymphoid  tissue  is  always  separated 
from  the  capsule  or  from  the  septa  by  a  distinct  space — the  lymph 
sinus — which  is  bridged  over  by  reticular  tissue  containing  compara- 


LYMPHATIC   ORGANS.  133 

tively  few  lymphoid  cells   (Fig.  75).      These   sinuses  form  a  contin- 
uous system  of  anastomosing  channels  throughout  the  node. 

The  reticular  connective  tissue  (page  73),  which  forms  a  part  of 
the  lymphatic  tissue  proper,  is  closely  attached  to  the  fibrous  connec- 
tive-tissue framework  of  the  organ.  In  the  lymph  nodules,  and  wher- 
ever the  lymphoid  cells  are  densely  packed,  the  underlying  reticular 
network  is  almost  completely  obscured.      Crossing  the  sinuses,  espe- 


priK 


3,° 


6    a 


'■ 


tJM^'^?  &  -f  \ 


FlG.  75.-Sectioii  through  Cortex  and  Portion  of  Medulla  of  Human  Lymph  Node.  X  350. 
(Technic  2,  p.  134.)  a,  Capsule  ;  b,  lymph  sinus  ;  c,  cells  showing  mitosis  ;  d,  germinal  cen- 
tre ;  e,  trabecular  ;  f,  blood-vessel  ;  g,  lymph  cords  :  A,  medulla  ;  i,  cortex. 

cially  those  of  the  medulla,  and  in  specimens  in  which  the  cells  have 
been  largely  washed  out  or  removed  by  maceration,  the  reticular 
structure  is  well  shown. 

The  lymphoid  tissue  proper,  as  represented  by  the  lymph  nodules 
and.  anastomosing  lymph  cords,  is  thus,  as  it  were,  suspended  in  the 
meshes  of  a  reticulum  which  is  swung  from  the  capsule  and  trabecu- 
lar. As  both  nodules  and  cords  are  everywhere  separated  from  cap- 
sule and  trabeculae  by  the  sinuses,  and  as  these  latter  serve  for  the 
passage  of  lymph  through  the  node,  it  is  seen  that  the  lymphatic  tis- 


134  THE   ORG  Ays. 

sue  of  the  node  is  broken  up  in  such  a  manner  as  to  be  bathed  on 
all  sides  by  the  circulating  lymph. 

In  addition  to  the  definitely  formed  lymph  nodes  and  the  well- 
defined  collections  of  lymph  nodules,  such  as  those  of  the  tonsil  or 
of  Peyer's  patches,  small  nodules  or  groups  of  lymphoid  cells  have  a 
wide  distribution  throughout  the  various  organs.  While  many  of 
these  collections  of  lymphatic  tissue  are  inconspicuous,  still  the  ag- 
gregate of  lymph  tissue  thus  distributed  is  by  no  means  inconsider- 
able. The  most  important  will  be  described  in  connection  with  the 
organs  in  which  they  occur. 

Blood-vessels. — Those  which  enter  the  hilum  carry  the  main  blood 
supply  to  the  organ.  Most  of  the  arteries  pass  directly  into  the  lym- 
phatic tissue,  where  they  break  up  into  dense  capillary  networks. 
Some  of  the  arteries,  instead  of  passing  directly  to  the  lymphatic  tis- 
sue, follow  the  septa,  supplying  these  and  the  capsule,  and  also  send- 
ing branches  to  the  surrounding  lymphatic  tissue.  A  few  small 
vessels  enter  the  capsule  along  the  convexity  of  the  organ  and  are 
distributed  to  the  capsule  and  to  the  larger  septa. 

Lymphatics. — The  afferent  lymph  vessels  enter  the  node  on  its 
convex  surface  opposite  the  hilum,  penetrating  the  capsule,  and  pour 
their  lymph  into  the  cortical  sinuses.  The  lymph  passes  through  the 
sinuses  of  both  cortex  and  medulla,  and  is  collected  by  the  efferent 
lymph  vessels  which  leave  the  organ  at  the  hilum.  Within  the  node 
the  lymph  comes  in  contact  with  the  superficial  cells  of  the  nodules 
and  of  the  lymph  cords.  These  cells  are  constantly  passing  out  into 
the  lymph  stream  so  that  the  lymph  leaves  the  node  much  richer  in 
cellular  elements. 

Nerves  are  not  abundant.  Hoth  medullated  and  non-medullated 
fibres  occur.      Their  exact  modes  of  termination  are  not  known. 

TECHNIC 

(r)  Remove  several  lymph  nodes  from  one  of  the  lower  animals  (ox,  cat,  dog, 
rabbit),  fix  in  formalin-Miiller's  fluid  (technic  5,  p.  5),  and  harden  in  alcohol. 
Cut  thin  sections  through  the  hilum,  stain  with  luvmatoxylin-eosin  (technic  1,  p. 
id),  or  with  hematoxylin  -  picro-  acid  -  fuchsin  (technic  3.  p.  16),  and  mount  in 
balsam. 

(2)  Expose  a  chain  of  lymph  nodules  {e.g.,  the  cervical  or  inguinal  of  a  re- 
cently killed  dog  or  cat).  Insert  a  small  cannula  or  needle  into  the  uppermost 
node  and  inject  formalin-Muller's  fluid  until  the  node  becomes  tense.  By  now 
slightly  increasing  the  pressure  the  fluid  maybe  made  to  pass  into  the  second  node, 
and  so  through  the  entire  chain.     The  nodes  are  then  carefully  dissected  out  and 


LYMPHATIC   ORGANS. 


135 


placed  for  twenty-four  hours  in  formalin- Aluller's  fluid,  then  hardened  in  alcohol. 
Sections  are  cut  through  the  hilum,  stained  with  haematoxylin-eosin  or  with  hasma- 
toxylin-picro-acid-fuchsin  and  mounted  in  balsam.  Near  the  centre  of  the  chain 
are  usually  found  nodes  in  which  the  lymph  sinuses  are  properly  distended.  The 
most  proximal  nodes  are  apt  to  be  overdistended.  but  for  this  very  reason  are 
often  excellent  for  the  study  of  the  reticular  tissue  from  which  most  of  the  cells 
have  been  washed  out,  especially  in  the  medulla. 

(3)  Human  lymph  nodes  may  be  treated  by  either  of  the  above  methods. 
Owing  to  the  coalescence  of  their  cortical  nodules  their  structure  is  apt  to  be  less 
easily  demonstrable  than  in  the  lower  animals. 

Haemolymph   Nodes. 

These  are  lymphoid  structures  which  ciosely  resemble  ordinary 
lymph  nodes,  but  with  the  essential  difference  that  their  sinuses  are 
blood  sinuses  instead  of  lymph  sinuses. 

Each  node  is  surrounded  by  a  capsule  of  varying  thickness,  com- 
posed  of  fibro-elastic  tissue  and  smooth   muscle  cells.      From  the 


FIG.   76.— Section  through  Human  Haemolymph  Gland,  including  Hilum,  showing  capsule, 
trabeculas,  sinuses  filled  with  blood,  and  lymph  nodules.     ( Warthin.) 

capsule  trabecules  of  the  same  structure  pass  down  into  the  node, 
forming  its  framework  (Fig.  76).  Beneath  the  capsule  is  a  blood 
sinus,  which   may  be  broad  or  narrow,  and   usually  completely  sur- 


136 


THE  ORGANS. 


rounds  the  node.  Less  commonly  the  sinus  is  interrupted  by  lym- 
phoid tissue  extending  out  to  the  capsule.  From  the  peripheral 
sinus  branches   extend  into  the   interior  of  the  node,  separating  the 


0£2  : 


FIG.  77.— Section  through  Superficial  Portion  of  Human  Haemolymph  Gland  (Marrow-lymph 
Gland).  (Warthin.)  Capsule,  trabeculae,  and  parts  of  two  adjacent  nodules;  sinuses 
filled  with  blood  ;  among  the  lymph  cells  are  large  multinuclear  cells  resembling  those  of 
marrow,  nucleated  red  blood  cells,  etc. 


lymphoid  tissue  into  cords  or  islands.  The  relative  proportion  of 
sinuses  and  lymphoid  tissue  varies  greatly,  some  nodes  being  com- 
posed almost  wholly  of  sinuses,  while  in  others  the  lymphoid  tissue 
predominates.  There  is  usually  a  fairly  distinct  Jiihim.  In  many 
glands  no  differentiation  into  cortex  and  medulla  can  be  made. 
Where  there  are  a  distinct  medulla  and  cortex  the  peripheral  lymphoid 
tissue  is  arranged  in  nodules  as  in  the  ordinary  lymph  node.  Re- 
ticular connective  tissue  crosses  the  sinuses  and  supports  the  cells  of 
the  lymph  nodules  and  cords  (Fig.  77). 

The  cellular  character  of  the  lymphoid  tissue  has  led  to  the  sub- 
division of  hx'iuolymph  nodes  into  splcnolymph  nodes  and  marrow- 
lymph  nodes.  In  the  splcnolymph  node  the  lymphoid  tissue  resembles 
that  of  the  ordinary  lymph  node  or  of  the  spleen.  In  the  marrow- 
lymph  node,  which  is  the  much  less  common  form,  the  lymphoid 
tissue   resembles  red   marrow.     There  are  no  distinct   nodules,  and 


LYMPHATIC  ORGANS.  137 

there  is  a  quite  characteristic  distribution  of  small  groups  of  fat  cells. 
The  most  numerous  cells  are  eosinophiles  and  mast  cells  (see  page 
87).  Polynuclear  leucocytes  and  large  leucocytes  with  a  single 
lobulated  nucleus  are  less  numerous.  The  very  large  multinuclear 
cells  of  red  marrow  are  also  found,  but  usually  in  small  numbers. 

Large  phagocytes  containing  blood  pigment  and  disintegrating  red 
blood  cells  are  found  in  both  forms  of  hasmolymph  nodes,  but  are 
most  numerous  in  the  splenolymph  type.  In  nodes  which  have  a 
brownish  color  when  fresh,  these  phagocytes  frequently  almost  com- 
pletely fill  the  sinuses. 

Further  classification  of  haemolymph  nodes  has  been  attempted, 
but  is  unsatisfactory,  owing  to  the  large  number  of  transitional 
forms.  Thus  many  nodes  are  transitional  in  structures  between  the 
haemolymph  node  and  the  ordinary  lymph  node,  between  the  spleno- 
lymph node  and  the  marrow-lymph  node,  and  between  the  spleno- 
lymph node  and  the  spleen. 

Under  normal  conditions  the  haemolymph  nodes  appear  to  be 
concerned  mainly  in  the  destruction  of  red  blood  cells ;  possibly  also 
in  the  formation  of  leucocytes.  Under  certain  pathological  con- 
ditions they  probably  become  centres  for  the  formation  of  red  blood 
cells. 

Blood-vessels. — An  artery  or  arteries  enter  the  node  at  the  hilum, 
and  break  up  within  the  node  into  small  branches,  which  communi- 
cate with  the  sinuses  where  the  blood  comes  into  intimate  association 
with  the  lymphoid  tissue.  From  the  sinuses  the  blood  passes  into 
veins,  which  leave  the  organ  either  at  the  hilum  or  at  some  other 
point  on  the  periphery.  The  course  which  the  blood  takes  in  pass- 
ing through  the  haemolymph  node  is  thus  apparently  similar  to  that 
taken  by  the  lymph  in  passing  through  the  ordinary  lymph  node. 

The  relation  of  the  haemolymph  node  to  the  lymp]iatic  system  is 
not  known,  and  like  ignorance  exists  as  to  its  innervation. 

TECHNIC. 

Same  as  for  lymph  nodes  (technic  1,  p.  134).  The  nodes  are  found  in  greatest 
numbers  in  the  prevertebral  tissue,  and  are  often  difficult  to  recognize.  Fixing  the 
tissues  in  5-per-cent  formalin  aids  in  their  recognition  as  it  darkens  the  nodes  while 
bleaching  the  rest  of  the  tissues. 


138  THE   ORGANS. 

The    Thymus. 

The  thymus  is  an  organ  of  foetal  and  early  extra-uterine  life, 
reaching  in  man  its  greatest  development  at  the  end  of  the  second 
year.  After  this  age  it  undergoes  a  slow  retrograde  change  into  fat 
and  connective  tissue,  until  by  the  twentieth  year  scarcely  a  vestige 
of  glandular  tissue  remains. 

The  thymus  originates  in  the  ectoderm  and  begins  its  foetal  exist- 
ence as  a  typical  epithelial  gland.  Into  this-  epithelial  structure 
mesodermic  cells  grow  and  differentiate  into  lymphatie  tissue.  This 
almost  completely  replaces  the  epithelial  tissue,  only  rudiments  of 
which  remain. 

Morphologically  the  fully  developed  thymus  consists  of  lobes  and 
lobules  (Fig.  78).  The  whole  gland  is  enclosed  in  a  single  con- 
nective-tissue capsule,  and  the  lobes  are  separated  from  one  another 


—  / 


FIG.  78.— From  Section  of  Human  Thymus,  showing1  parts  of  five  lobules  and   interlobular 
<  20.     (Technic,  page  139.)     a,  Cortex  ;  /',  medulla;  c,  interlobular  septum. 

by  strong  extensions  of  capsular  tissue.  Smaller  connective-tissue 
septa  extend  into  the  lobes,  subdividing  them  into  lobules.  From 
the  perilobular  connective  tissue,  septa  extend  into  the  lobule,  sepa- 
rating it  into  a  number  of  chambers.  Each  lobule  consists  of  a  cor- 
tical portion  and  a  medullary  portion.     The  cortex  consists  of  nodules 


LYMPHATIC   ORGANS.  139 

of  compact   lymphatic   tissue   similar   to   those  found   in   the  lymph 
node.      These  occupy  the  chambers  formed  by  the   connective-tissue 
septa.      The  medulla  consists  of  a  more  diffuse  lymphatic  tissue  with 
no  connective-tissue  septa.      In  the  medulla  are  found  a  number  of 
spherical    or   oval    bodies   com- 
posed of  concentrically  arranged 
epithelial       cells.      These      are 
known    as    HassaV s    corpuscles 
(Fig.    79),    and    represent    the 
only    remains    of    the    original 
glandular  epithelium.     The  cen- 
tral cells  of  the  corpuscles  are 
usually    spherical    and    contain 
nuclei,     while     the     peripheral  '         a 

cells  are  flat  and  non-nucleated.  "    -    c- 

Unlike  the    Other    lymphatic       Fig.  79.— Hassal's  Corpuscle  and  S mall  Portion 

, -,  ,  -,  -,     ,  r  of  Surrounding- Tissue,     X  600.     (Seetechnic 

organs,    the    lymph    nodules   of        below.) 

the  thymus  contain  no  germinal 

centres.      Mitosis    can,    however,  usually   be    seen    in   the  lymphoid 

cells.      Nucleated  red   blood   cells  also    occur  in  the    thymus.      The 

thymus  must  therefore  be  considered  one  of  the  sources  of  lymphoid 

cells  and  of  red  blood  cells. 

Blood-vessels. — The  larger  arteries  run  in  the  connective-tissue 
septa.  From  these,  smaller  intralobular  branches  are  given  off,  which 
break  up  into  capillary  networks  in  the  cortex  and  medulla.  The 
capillaries  pass  over  into  veins.  These  converge  to  form  larger  veins, 
which  accompany  the  arteries. 

Of  the  lymphatics  of  the  thymus  little  is  known.  They  appear 
to  originate  in  indefinite  sinuses  within  the  lymphoid  tissue,  whence 
they  pass  to  the  septa,  where  they  accompany  the  blood-vessels. 

Nerves. — These  are  distributed  mainly  to  the  walls  of  the  blood- 
vessels. A  few  fine  fibres,  terminating  freely  in  the  lymphatic  tissue 
of  the  cortex  and  of  the  medulla,  have  been  described. 

TECHNIC. 

Fix  the  thymus  of  a  new-born  infant  in  formalin-Miiller's  fluid  (technic  5,  p. 
5),  and  harden  in  alcohol.  Stain  sections  with  haematoxylin-eosin  (technic  1, 
p.  16),  or  with  haematoxylin-picro-acid-fuchsin  (technic  3.  p.  16),  and  mount  in 
balsam . 


140  THE   ORGANS. 


The  Tonsils. 


The  Palatine  Tonsils  or  True  Tonsils. — These  are  compound 
lymphatic  organs,  essentially  similar  in  structure  to  the  lymphatic 
organs  already  described.  The  usual  fibrous  capsule  is  present  only 
over  the  attached  surface,  where  it  separates  the  tonsil  from  sur- 
rounding structures.  From  the  capsule,  connective-tissue  trabecules 
extend  into  the  substance  of  the  organ  and  branch  to  form  its  frame- 
work. The  free  surface  of  the  tonsil  is  covered  by  a  reflection  of  the 
stratified  squamous  epithelium  of  the  pharynx  (Fig.  80).      The  epithe- 


y 


Fig.  80.— Vertical  Section  of  Dor's  Tonsil  through  Crypt.  X  15.  (Szymonowicz.)  a,  Lymph 
nodule;  f>,  epithelium  of  crypt;  c,  blood-vessel;  d,  crypt;  e,  connective-tissue  capsule; 
/",  mucous  glands  ;  g,  epithelium  of  pharynx. 

lium  is  separated  from  the  underlying  lymphatic  tissue  of  the  tonsil 
by  a  more  or  less  distinct  basement  membrane.  At  several  places  on 
the  surface  of  the  tonsil  deep  indentations  or  pockets  occur.  These 
are  known  as  the  crypts  of  the  tonsil  (Fig.  80),  and  are  lined  through- 


LYMPHATIC   ORGANS. 


141 


out  by  a  continuation  of  the  surface  epithelium.  Passing  off  from 
the  bottoms  and  sides  of  the  main  or  primary  crypts  are  frequently 
several  secondary  crypts,  also  lined  with  the  same  type  of  epithelium. 
Beneath  the  basement  membrane  is  the  lymphoid  tissue  of  the 
tonsil.     This  consists  of  diffuse  lymphatic  tissue  in  which  are  found 


FlG.  81. — Vertical  Section  through  Wall  of  Crypt  in  Dog's  Tonsil,  showing  lymphoid  infiltra- 
tion of  epithelium.  X  150.  (Bohm  and  von  Davidoff.)  a,  Leucocytes  in  epithelium  ;  b, 
space  in  epithelium  filled  with  leucocytes  and  changed  epithelial  cells  ;  c,  blood-vessel ; 
d,  epithelium  beyond  area  of  infiltration  ;  e,  basal  layer  of  cells. 


nodules  of  compact  lymphatic  tissue  similar  to  those  in  the  lymph 
node.  Each  nodule  has  a  germ  centre,  where  active  mitosis  is  going 
on,  and  a  surrounding  zone  of  more  densely  packed  cells.  The 
nodules  have  a  fairly  definite  arrangement,  usually  forming  a  single 
layer  beneath  the  epithelium  of  the  crypts.  At  various  points  on  the 
surface  of  the  tonsil,  and  especially  in  the  crypts,  occurs  what  is 
known  as  lymphoid  infiltration  of  the  epithelium  (Fig.  81).  This 
consists  in  an  invasion  of  the  epithelium  by  the  underlying  lymphoid 
cells.  It  varies  from  the  presence  of  only  a  few  lymphoid  cells  scat- 
tered among  the  epithelial,  to  an  almost  complete  replacement  of  epi- 
thelial by  lymphoid  tissue.  In  this  way  the  latter  reaches  the  sur- 
face and  lymphoid  cells  are  discharged  upon  the  surface  of  the  tonsil 
and  into  the  crypts.  These  cells  probably  form  the  bulk  of  the  so- 
called  salivary  corpuscles. 

The  Lingual  Tonsils — Folliculi  Linguales. — These  are  small 
lymphatic  organs  situated  on  the  dorsum  and  sides  of  the  back  part 
of  the  tongue,  and  are  similar  in  structure  to  the  true  tonsils.  Into 
their  crypts  frequently  open  the  ducts  of  some  of  the  mucous  glands 
of  the  tongue. 


142  THE   ORGANS. 

The  Pharyngeal  Tonsils. — These  are  lymphatic  structures  which 
lie  in  the  nasopharynx.      They  resemble  the  lingual  tonsils. 

The  tonsils  make  their  first  appearance  toward  the  end  of  the 
fourth  month  of  intra-uterine  life.  The  earliest  of  the  tonsillar  lym- 
phoid cells  are  white  blood  cells  which  have  migrated  from  the  ves- 
sels of  the  stroma  of  the  mucosa  and  have  infiltrated  the  surrounding 
connective  tissue.  Further  development  of  the  tonsil  is  by  prolif- 
eration of  these  cells.  The  crypts  are  at  first  solid  ingrowths  of  sur- 
face epithelium.      These  later  become  hollowed  out. 

The  blood-vessels  and  nerves  have  a  distribution  similar  to  those 
of  the  lymph  nodes,  but  enter  the  organ  on  its  attached  side  and  not 
at  a  definite  hilum. 

Of  the  lymphatics  of  the  tonsil  little  is  known. 

TECHNIC. 

Normal  human  tonsils  are  so  rare,  owing  to  the  frequency  of  inflammation  of 
the  organ,  that  it  is  best  to  make  use  of  tonsils  from  one  of  the  lower  animals  (dog, 
cat,  or  rabbit).  Treat  as  in  technic  i,  p.  134.  care  being  taken  that  sections  pass 
longitudinally  through  one  of  the  crypts. 

The   Spleen. 

The  spleen  is  a  lymphatic  organ,  the  peculiar  structure  of  which 
appears  to  depend  largely  upon  the  arrangement  of  its  blood-vessels. 

The  surface,  except  where  the  organ  is  attached,  is  covered  by  a 
serous  membrane,  the  peritoneum  (page  129).  Beneath  this  is  a  cap- 
sule of  fibrous  tissue  containing  numerous  elastic  fibres  and  smooth 
muscle  cells.  From  the  capsule  strong  connective-tissue  septa,  simi- 
lar to  the  capsule  in  structure,  extend  into  the  interior  of  the  organ. 
These  branch  and  unite  with  one  another  to  form  a  series  of  anasto- 
mosing chambers.  The  capsule  and  septa  form,  as  in  the  lymph 
node,  the  connective-tissue  framework  of  the  organ  (Fig.   82). 

The  chambers  formed  by  the  connective-tissue  framework  are 
filled  in  with  lymphatic-  tissue,  which  occurs  in  two  forms,  diffuse  and 
compact.  The  diffuse  lymphatic  tissue  constitutes  the  substantia 
propria  of  the  organ  and  is  everywhere  traversed  by  thin-walled  vas- 
cular channels,  the  lymphatic  tissue  and  vascular  channels  together 
constituting  the  splenic  pulp  (Fig.  83).  Compact  lymphatic  tissue 
occurs  as  spherical,  oval,  or  cylindrical  aggregations  of  closely  packed 
lymphoid   cells.     These  are  known  as  Malpighian  bodies  or  splenic 


LYMPHATIC   ORGANS. 


143 


corpuscles  (Figs.  82  and  83)  and  are  distributed  throughout  the  splenic 
pulp.      Each  splenic  corpuscle  contains  one  or  more  small  arteries. 


Fig.  82. — Section  through  Portion  of  Cat's  Spleen,  to  show  general  topographv.  X  15. 
(Technic  1,  p.  146.)  J,  Capsule  ;  b,  trabeculse  containing  blood-vessels  ;  c,  germinal  centres  ; 
d,  trabeculse;  <?,  lymph  nodules. 

These  usually  run  near  the  periphery  of  the  corpuscle ;  more  rarely 
they  lie  at  the  centre.  Except  for  its  relation  to  the  blood-vessels, 
the  splenic  corpuscle  is  quite  similar  in  structure  to  a  lymph  nodule. 


-■)-!-' 


.\  i  C"..i    L"\-,     ^- c.r'V  O '-       :''".■!""   -■->•?.•)   ~J?-'~~i  '--', 


&•; 


*j^,:Sl.:'.  V *! 


3  ,  ^ 
,/  a 


Fig.  83.— Section  of  Human  Spleen,  including  portion  of  Malpighian  body  with  its  artery  and 
adjacent  splenic  pulp.  X  300.  (Technic  2,  p.  146.)  <?,  Malpighian  body;  b,  pulp  cords,  c, 
cavernous  veins  ;  b  and  c  together  constituting  the  splenic  pulp. 

It  consists  of   lymphoid  cells   so   closely  packed   as    completely   to 
obscure  the  underlying  reticulum.      In  the  centre  of  each  corpuscle 


144 


THE   ORGANS. 


is  a  germinal  centre  (see  page  132).      The  blood-vessels  of  the  spleen 
have   a   very   characteristic   arrangement,  which   must   be   described 

before  considering;  further   the 


B 


J? 


E 


J 

'-few- ■-:■■ 


Fig.  84. — Isolated  Spleen  Cells.  X  700.  (Kolli- 
ker.)  .4,  Cell  containing  red  blood  cells;  I', 
blood  cell;  /c,  nucleus;  B,  leucocyte  with 
polymorphous  nucleus;  C,  "spleen"  cell 
with  pigment  granules  ;  D,  lymphocyte  ;  E, 
large  cell  with  lobulated  nucleus  (megalo- 
cyte )  :  F,  nucleated  red  blood  cells  ;  G,  red 
blood  cells;  //,  multinuclear  leucocyte;  J, 
cell  containing  eosinophile  granules. 


minute  structure  of  the  organ. 

The  arteries  enter  the  spleen 
at    the    hilum    and    divide,    the 
branches  following  the  connec- 
tive-tissue septa.     The  arteries 
are     at     first     accompanied    by- 
branches   of    the    splenic  veins. 
Soon,      however,     the     arteries 
leave  the    veins   and  the  septa 
and    pursue    an    entirely    sep- 
arate course  through  the  splenic 
pulp.      Here  the    adventitia   of 
the    smaller    arteries    assumes 
the  character  of  reticular  tissue 
and    becomes     infiltrated    with 
lymphoid  cells.      In  certain  an- 
imals, as,  e.g.,   the  guinea-pig, 
this    infiltration    is    continuous,   forming   long    cord-like  masses    of 
compact    lymphoid    tissue.      In    man,    the    adventitia    is    infiltrated 
only  at  points  along  the  course  of  an  artery.      This  may  take  the 
form    of    elongated    collections    of    lymphoid    cells — the    so-called 
spindles — or  of  distinct  lymph  nodules,  the  already  mentioned  splenic 
corpuscles.     Although   usually  eccentrically  situated  with   reference 
to  the  nodules,  these  arteries  are  known  as  central  arteries.     They 
give  rise  to  a  few  capillaries  in  the  spindles,  to  a  larger  number  in 
the    nodules.      Beyond    the    latter,    the    arteries    divide    into    thick- 
sheathed  terminal  arteries — ellipsoids — which  do  not  anastomose,  but 
lie  close  together  like  the  bristles  of  a  brush  or  pcnicillus.     The  ter- 
minal arteries  break  up  into  arterial  capillaries  which  still  retain  an 
adventitia,  and  which  empty  into  broader  spaces — sinuses  or  ampulla? 
— which  in  turn  empty  into  the  cavernous  veins  of  the  splenic  pulp. 

The  Splenic  Pulp. — The  anastomosing  cavernous  veins  break 
up  the  diffuse  lymphatic  tissue  of  the  spleen  into  a  series  of  anasto- 
mosing cords  similar  to  those  found  in  the  medulla  of  the  lymph 
node.  These  are  known  as  pulp  cords  (Fig.  83),  and  with  the  cavern- 
ous veins  constitute  the  splenic  pulp.     The  pulp  cords   consist  of  a 


LYMPHATIC   ORGANS. 


145 


delicate  framework  of  reticular  connective  tissue,  in  the  meshes  of 
which  are  found  the  following  varieties  of  cells  (Fig.  84) : 

(1)  Red  blood  cells. 

(2)  Nucleated  red  blood  cells. 

(3)  White  blood  cells. 

(4)  Mononuclear  cells,  the  so-called  spleen  cells.  These  are 
rather  large  granular,  spherical,  or  irregular  cells.  From  the  fact 
that  blood  pigment  and  red  blood  cells  in  various  stages  of  disinte- 
gration are  found  in  their  cytoplasm,  these  cells  are  believed  to  be 
concerned  in  the  destruction  of  red  blood  cells. 

(5)  M'ultimiclear  cells.  These  are  most  common  in  young  ani- 
mals. Each  cell  contains  a  single  large  lobulated  nucleus,  or  more 
frequently  several  nuclei.  These  cells  resemble  the  osteoclasts  of 
developing  bone  and  the  multinuclear  cells  of  bone  marrow. 

In  macerated  splenic  tissue  or  in  smears  from  the  spleen,  there 
are  found,  in  addition  to  the  above  varieties  of  cells,  long  spindle- 
shaped  cells  with  bulging 
nuclei.  These  come  from  the 
walls  of  the  cavernous  veins. 


Two  views  are  held  re 
garding  the  vascular  channels 
of  the  splenic  pulp.  Accord- 
ing to  one,  these  channels 
have  complete  walls,  the 
arterial  capillaries  passing 
over  into  venous  capillaries 
in  the  usual  manner ;  accord- 
ing to  the  other,  the  arterial 
capillaries  open  into  spaces, 
the  cavernous  veins  or  spleen 
sinuses  which  have  fenes- 
trated walls,  thus  allowing 
the  blood  to  come  into  direct 
contact  with  the  surrounding 
tissues.  From  these  open- 
walled  sinuses,  the  veins  prop- 
er take  origin.  These  unit- 
ing form  veins  which  enter  the  septa  and  ultimately  converge  to 
form  the  splenic  veins  which  leave  the  organ  at  the  hilum. 

According  to  Mall,  the  spleen,  like  the  liver,  is  composed  of  a 
large  number  of  lobules,  which  may  be  considered  its  anatomical 
units   (Fig.    85).     Each   lobule   is   separated  from  its  neighbors  by 


Fig.  85.—  Diagram  of  Splenic  Lobule,  according  to 
Mall,  a,  Capsule  ;  b,  intralobular  venous  spaces; 
c,  intralobular  vein  ;  d,  ampulla  of  Thoma  ;  e, 
pulp  cord  ;/,  interlobular  vein  ;  g,  intralobular 
vein  ;  //,  Malpighian  body ;  /,  intralobular  tra- 
becula  ;  /,  interlobular  trabecula  ;  A\  intralob- 
ular artery  ;  /,  artery  to  one  of  the  ten  compart- 
ments;  «z,  intralobular  trabecula. 


146  THE   ORGANS. 

several  (usually  three")  connective-tissue  septa  (interlobular  septa). 
Each  interlobular  septum  gives  off  about  three  secondary  septa  (in- 
tralobular septa)  which  pass  into  the  lobule  and,  anastomosing, 
divide  it  into  about  ten  chambers,  which  are  filled  with  splenic 
pulp.  As  the  splenic  pulp  of  neighboring  chambers  anastomoses, 
cord-like  structures  are  formed  which  Mall  designates  pulp  cords.  It 
will  be  seen  that  the  pulp  cords  of  Mall  are  altogether  different  from 
the  pulp  cords  previously  mentioned.  An  artery  passes  through  the 
centre  of  each  lobule,  giving  off  a  branch  to  each  of  its  chambers. 
These  branch  repeatedly  in  the  pulp  cords  of  Mall  and  end  in  small 
dilatations,  the  ampullar  of  Thoma.  The  ampullae  pass  over  into 
minute  veins  which  converge  and. empty  into  the  interlobular  veins. 
Mall  believes  the  walls  of  the  ampullae  and  beginning  venous  plexuses 
to  be  very  porous,  "  allowing  fluids  to  pass  through  with  great  case 
and  granules  only  with  difficulty."  He  further  states  that  "  in  life 
the  plasma  constantly  flows  through  the  intercellular  spaces  of  the 
pulp  cords,  while  the  blood  corpuscles  keep  within  fixed  channels." 

Lymphatics  are  not  numerous.  In  certain  of  the  lower  animals 
large  lymph  vessels  occur  in  the  capsule  and  septa.  These  are  not 
well  developed  in  man.  Lymph  vessels  are  present  in  the  connective 
tissue  of  the  hilum.  They  probably  do  not  occur  in  the  splenic  pulp 
or  in  the  corpuscles. 

Nerves. — These  are  mainly  of  the  non-medullated  variety,  al- 
though a  few  medullated  fibres  are  present.  The  latter  are  dendrites 
of  sensory  neurones  whose  cell  bodies  are  situated  in  the  spinal  gan- 
glia. They  supply  the  connective  tissue  of  the  capsule,  septa,  and 
blood-vessels.  The  non-medullated  fibres — axones  of  sympathetic 
neurones — accompany  the  arteries,  around  which  they  form  plexuses. 
From  these  plexuses  terminals  pass  to  the  muscle  cells  of  the  arteries, 
to  the  septa,  to  the  capsule,  and  possibly  also  to  the  splenic  pulp. 
The  exact  manner  in  which  both  medullated  and  non-medullated 
fibres  terminate  is  as  yet  undetermined. 

TECHNIC. 

(\)  The  spleen  of  a  cat  is  more  satisfactory  for  topography  than  the  human 
spleen,  as  it  is  smaller,  contains  more  connective  tissue,  and  its  Malpighian  bodies 
are  more  evenly  distributed  and  more  circumscribed.  Fix  in  formalin-Midler's 
fluid  (technic  5,  p.  5),  and  harden  in  alcohol.  Cut  sections  through  the  entire 
spleen.  Stain  with  haematoxylin-eosin  (technic  1,  p.  16),  or  with  haematoxylin- 
picro-acid  fuchsin  (technic  3,  p.  16). 

(2)  Human  Spleen. — Small  pieces  are  treated  as  in  technic  (1). 

(3)  Human  Spleen  (Congested). — Congested  human  spleens  are  usually  easy  to 
obtain  from    autopsies.     Treat   as  in  technic  (1).     The  cavernous  veins  being  (lis- 


LYMPHATIC   ORGANS.  147 

tended  with  blood,  the  relations  of  the  veins  to  the  pulp  cords  are  more  easily  seen 
than  in  the  uncongested  spleen.  The  contrasts  are  especially  sharp  in  sections 
stained  with  haematoxylin-picro-acid-fuchsin. 

(4)  The  cells  of  the  spleen  may  be  studied  along  the  torn  edges  or  in  the  thin- 
ner parts  of  any  of  the  spleen  sections.  Or  a  smear  may  be  made  in  a  manner 
similar  to  that  described  in  technic  (page  90),  by  drawing  the  end  of  a  slide  across 
a  freshly  cut  spleen  surface  and  then  smearing  the  tissue  thus  obtained  across  the 
surface  of  a  second  slide.  Dry,  fix  in  equal  parts  alcohol  and  ether  (one-half  hour), 
stain  with  haematoxylin-eosin  and  mount  in  balsam.  Or  the  cut  surface  of  the 
spleen  may  be  scraped  with  a  knife,  the  scrapings  transferred  to  Zenker's  rluid, 
hardened  in  alcohol,  stained  with  alum-carmine  (pages  15  and  90)  and  mounted  in 
eosin-giycerin. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen,  vol.  iii. 

Szymonowicz  and  MacCallum  :  Histology  and  Microscopic  Anatomy. 

Warthin  :  Haemolymph  Glands  (with  bibliography).  Reference  Handbook  of 
the  Medical  Sciences,  vol.  iv. 

Mall:  Lobule  of  the  Spleen.  Bui.  Johns  Hopkins  Hospital,  vol.  ix.  —  Archi- 
tecture and  Blood-vessels  of  the  Dog's  Spleen.     Zeit.  f.  Morph.  u.  An'th.,  Bd.  ii. 

Oppel:  Ueber  Gitterfasern  der  menschlichen  Leber  und  Milz.  Anat.  Anz.,  6 
Jahrg.,  S.  165. 


CHAPTER    III. 

THE    SKELETAL    SYSTEM. 

The  skeletal  system  consists  of  a  series  of  bones  and  cartilages 
which  are  united  by  special  structures  to  form  the  supporting  frame- 
work of  the  body.  Under  this  head  are  considered:  (i)  bones,  (2) 
marrow,  (3)  cartilages,  (4)  articulations. 

The   Bones. 

A  bone  considered  as  an  organ  consists  of  bone  tissue  laid 
down  in  a  definite  and  regular  manner.  If  a  longitudinal  section 
be  made  through  the  head  and  shaft  of  a  long  bone,  the  head  of 
the  bone  and  inner  part  of  the  shaft  are  seen  to  be  composed  of 
anastomosing  bony  trabecular  enclosing  cavities.  This  is  known 
as   cancellous  or  spongy  bone.      The  shaft  of  the   bone  consists  of  a 


i£  * 


Fig.  86.— Section  of  Spongy  Bone.    X  75.     (Technic  3,  p.  156.)     a,  Marrow  space  ;  t>,  group  of  fat 
cells  ;  c,  blood-vessel  ;  d,  trabecular  of  bone. 

large  central  cavity  surrounded  by  spongy  bone,  which,  however, 
passes  over  on  its  outer  side  into  a  layer  of  bone  of  great  hardness 
and   known  as   hard  or  compact  bone.      Spongy  bone  forms  the  ends 

148 


THE  SKELETAL   SYSTEM. 


149 


and  lines  the  marrow  cavities  of  the  long  bones,  and  forms  the  centre 
of  the  short  and  flat  bones.  Compact  bone  forms  the  bulk  of  the 
shafts  of  the  long  bones  and  the  outer  layers  of  the  flat  and  short 
bones. 

In  compact  bone  the  layers  or  lamellae  of  bone  tissue  have  a  defi- 
nite arrangement   into  systems,  the  disposition  of  which   is   largely 


Fig.  87. 


-Longitudinal   Section  of  Hard  (Undecalcified  Bone)  Shaft  of  Human  Ulna.     X  90. 
(Szymonowicz.)     Haversian  canals,  lacunas,  and  canaliculi  in  black. 


dependent  upon  the  shape  of  the  bone  and  upon  the  distribution  of 
its  blood-vessels. 

In  spongy  bone  (Fig.  S6)  there  is  no  arrangement  of  the  bone  tis- 
sue into  systems.  The  trabecular  consist  wholly  of  bony  tissue  laid 
down  in  lamellae.  These  trabecular  anastomose  and  enclose  spaces 
which  contain  marrow  and  which  serve  for  the  passage  of  blood-ves- 
sels, lymphatics,  and  nerves. 

On  examining  a  longitudinal  section  of  compact  bone  (Fig.  87) 
.there  are  seen  running  through  it  irregular  channels,  the  general 
direction  of  which  is  parallel  to  the  long  axis  of  the  bone.  These 
channels  anastomose  by  means  of  lateral  branches,  and  form  a  com- 


150  THE   ORGANS, 

plete  system  of  intercommunicating  tubes.  They  are  known  as 
Haversian  canals,  contain  marrow  elements,  and  serve  for  the  trans- 
mission of  blood-vessels,  lymphatics,  and  nerves.     They  anastomose 


—  .-4  tffe  •>'     >  < 


■'■'. 


*a*g 


FlG.  88 —Cross  section  of  Hard  ( Un'iecalcified )  Bone  from  Human  Metatarsus.  X  90.  (Szy- 
monowicz.)  Haversian  canals,  lacunas,  and  canaliculi  ill  black,  a,  Outer  circumferential 
lamellae  ;  />,  inner  circumferential  lamellae  ;  c,  Haversian  lamella;  ;  if,  interstitial  lamellaa. 

not  only  with  one  another,  but  are  in  communication  with  the  surface 
of  the  bone  and  with  the  marrow  cavity.  Between  the  Haversian 
canals  the  lamellae  are  seen  running  parallel  to  the  canals. 

In  a  cross  section  through  the  shaft  of  a  long  bone  (Fig.  88), 
three  distinct  systems  of  lamella:  are  seen.  These  are  known  as 
Haversian  lamella,  interstitial  lamella?,  wad  circumferential  lamella. 

0)  Haversian  Lamellae  (Fig.  89). — These  are  arranged  in  a 
concentric  manner  around  the  Haversian  canals.  Between  the 
lamellae,  their  long  axes  corresponding  to  the  long  axes  of  the  Haver- 


THE  SKELETAL   SYSTEM. 


151 


sian  canals,  are  the  lacuna  with  their  enclosed  bone  cells  (page  83). 
The  lacunae  of  adjacent  lamellae  are  usually  arranged  alternately.  In 
a  section  of  ordinary  thickness  the  lacunae  are  not  nearly  so  numerous 
as  the  lamellae,  and  are  seen  only  between  some  of  the  lamellae. 
The  lacunae  of  a  Haversian  system  communicate  with  one  another 
and  with  their  Haversian  canal  by  means  of  the  canaliculi.  In 
Haversian  systems  the  fibres  of  the  matrix  (see  page  S3)  run  in 
some  lamellae  parallel  to  the  canal,  in  others  concentrically.  Adja- 
cent fibres  thus  frequently  cross  at  right  angles.  The  Haversian 
canal  itself  contains  marrow,  blood-vessels,  lymphatics,  and  nerves. 

(2)  Interstitial  (Intermediate  or  Ground)  Lamell.e  (Figs. 
88  and  89). — These  are  irregular  short  lamellae,  which  occupy  the 
spaces  left  between  adjacent 
Haversian  systems. 

(  3 )  Circumferential 
Lamellae  (Fig.  8S). — These 
are  parallel  lamellae  which 
run  in  the  long  axis  of  the 
bone,  just  beneath  the  peri- 
osteum and  at  the  outer  edge 
of  the  marrow  cavity.  Occa- 
sionally circumferential  lam- 
ellae are  absent,  the  Haversian 
systems  abutting  directly 
upon  periosteum. 

Channels  for  the  passage 
of  blood-vessels  from  the 
periosteum  to  the  Haversian 
canals  pierce  the  circumfer- 
ential lamellae.  They  are 
known  as  Volkmann '  s  canals, 
and  are  not  surrounded  by 
concentric  lamellae  as  are 
the  Haversian  lamellae,  but 
are  mere  channels  through 
the  bone.  Similar  canals  pass  from  the  inner  Haversian  canals  into 
the  marrow  cavity. 

The  Periosteum. — This  is  a  fibrous  connective-tissue  membrane 
which  covers  the  surfaces  of  bones  except  where  they  articulate.      It 


Fig.  89. — Transverse  Section  of  Compact  Bone 
from  Shaft  of  Humerus.  X  150  and  slightly  re- 
duced. (Sharpey.)  (Technic  1,  p.  S3. 1  Three 
Haversian  canals  with  their  concentric  lamellae 
and  lacunae  ;  canaliculi  connecting  lacunae  with 
each  other  and  with  Haversian  uanal.  Between 
ihe  Haversian  systems  of  lamellae  are  seen  the 
interstitial  lamellae. 


152  THE   ORGANS. 

is  firmly  adherent  to  the  superficial  layers  of  the  bone  and  consists 
of  two  layers.  The  outer  layer  is  composed  of  coarse  fibrillated 
fibres  and  contains  the  larger  blood-vessels.  The  inner  layer  consists 
of  fine  white  fibres  and  delicate  elastic  fibres  which  support  the 
smaller  blood-vessels. 

From  the  periosteum  distinct  bundles  of  white  fibres,  with  often 
some  elastic  fibres,  pierce  the  outer  layers  of  the  bone.  These  are 
known  as  the  perforating  fibres  of  Sharpey.  When  tendons  and 
ligaments  are  attached  to  bone,  their  fibres  are  prolonged  through  the 
periosteum  into  the  bone  as  perforating  fibres. 

Bone   Marrow. 

Bone  marrow  is  a  soft  tissue  which  occupies  the  medullary  and 
Haversian  canals  of  the  long  bones  and  fills  the  spaces  between  the 
trabecules  of  spongy  bone.  Marrow  occurs  in  two  forms — red  mar- 
row and  yellow  marrow. 

Red  marrow  is  found  in  all  bones  of  embryos  and  of  young  ani- 
mals, also  in  the  vertebras,  sternum,  ribs,  cranial  bones,  and  epiphyses 
of  long  bones  in  the  adult.  In  the  diaphyses  of  adult  long  bones  the 
marrow  is  of  the  yellow  variety.  The  difference  in  color  between 
red  marrow  and  yellow  marrow  is  clue  to  the  much  greater  proportion 
of  fat  in  the  latter,  yellow  marrow  being  developed  from  the  red  by 
an  almost  complete  replacement  of  its  other  elements  by  fat  cells. 

Red  marrow  is  of  especial  interest  as  a  blood-forming  tissue, 
being  in  the  healthy  adult  the  main  if  not  the  sole  source  of  red 
blood  cells,  and  one  of  the  sources  from  which  the  leucocytes  are 
derived.  The  blood-forming  function  of  marrow  must  be  borne  in 
mind  in  studying  the  various  forms  of  marrow  cells. 

Red  marrow  (Fig.  90)  consists  of  a  delicate  reticular  connective 
tissue  which  supports  the  following  varieties  of  cells : 

(1)  Marrow  Cells — Myelocytes. — These  resemble  the  mononu- 
clear and  some  of  the  transitional  forms  of  leucocytes.  The  nucleus 
is  large  and  may  be  lobulated.  It  contains  a  comparatively  small 
amount  of  chromatin  and  therefore  stains  faintly.  The  cytoplasm  is 
finely  granular  and  stains  with  neutrophile  dyes.  Myelocytes  are  not 
present  in  normal  blood,  but  occur  in  large  numbers  in  leukxmia. 
It  is  from  the  myelocytes  that  those  leucocytes,  which  are  of  bone- 
marrow  origin,  are  derived. 


THE  SKELETAL   SYSTEM. 


153 


(2)  Nucleated  Red  Blood  Cells.  — These  are  divisible  into  erythro- 
blasts  and  normoblasts.  The  former  represents  an  earlier,  the  latter 
a  later  stage  in  the  evolution  of  the  non-nucleated  adult  red  blood 
cell. 

The  erythroblast,  the  younger  of  the  two,  has  a  well-formed  nu- 
cleus with  a  distinct  intranuclear  network.  The  protoplasm  contains 
but  little  haemoglobin.      In  the  normoblast  the  intranuclear  network 


—  b 


gp 


..:-.--.-.  d 


e  f 

FIG.  go.— Section  of  Red  Bone  Marrow  from  Rabbit's  Femur.  X  700.  (Technic  4,  p.  156.)  a, 
Fat  cells  ;  b,  myeloplax  ;  c,  fat  space  ;  d,  nucleated  red  blood  cells  ;  e,  myelocytes  ;  f,  re- 
ticular connective  tissue  ;  g,  leucocytes. 


has  disappeared  and  the  protoplasm  has  become  much  richer  in  hae- 
moglobin. The  normoblast  is  converted  into  the  adult  red  blood 
cell  either  by  extrusion  of  its  nucleus  or  by  the  disintegration  of  the 
nucleus  within  the  cell  body. 

(3)  Non-Nucleated  Red  Blood  Cells. — These  are  the  same  as  are 
found  in  the  blood  (page  85). 

(4)  Multinuclear  Cells — Myeloplaxes. — These  are  large  cells  with 
abundant  protoplasm.  Each  cell  may  contain  a  single  large  spheri- 
cal nucleus  or  a  much   lobulated  nucleus  or  several  nuclei.      Myelo- 


154 


THE   ORGANS. 


plaxes  are  probably  derived  from   leucocytes,  and  are  closely  related 
to,  if  not  identical  with,  the  osteoclasts  of  developing  bone. 

(5)  Eosinopkile  cells  are  frequently  found  in  marrow.     They  have 
the  same  structure  as  in  blood  (page  8y). 

(6)  Mast  ails  may  be  present.     They  are   usually  not  numerous. 
(For  description  see  page  88.) 

(7)  Fat  Cells. — These  are  usually  round  and  rather  evenly  distrib- 
uted throughout  the  marrow. 

Yellow  marrow  (Fig.  91)  consists  almost  wholly  of  fat   cells, 
which  have  gradually  replaced  the  other  marrow  elements.      Under 


PlG.  91,  Yellow  Marrow  from  Rabbit's  Femur.  X  560.  (Technic  4,  p.  156.)  a.  Nucleated  red 
blood  cells;  b,  myeloplax,  c,  fat  celis  ;  </,  myelocytes;  e,  reticular  connective  tissue;  /, 
leucoi 


certain  conditions  the  yellow  marrow  of  the  bones  of  the  old  or  great- 
ly emaciated  undergoes  changes  due  for  the  most  part  to  the  absorp- 
tion of  its  fat.  Such  marrow  becomes  reddish  and  assumes  a  some- 
what gelatinous  appearance.      It  is  known  as  "gelatinous  marrow T 


THE  SKELETAL   SYSTEM.  155 

The  large  marrow  cavities,  such  as  those  of  the  shafts  of  the  long 
bones,  are  lined  by  a  layer  of  fibrous  connective  tissue,  the  cndosteum. 

Blood-vessels. — The  blood-vessels  of  bone  pass  into  it  from  the 
periosteum.  Near  the  centre  of  the  shaft  of  a  long  bone  a  canal 
passes  obliquely  through  the  compact  bone.  This  is  known  as  the 
nutrient  canal  and  its  external  opening  as  the  nutrient  foramen. 
This  canal  serves  for  the  passage  of  the  nutrient  vessels — .usually 
one  artery  and  two  veins — to  and  from  the  medullary  cavity.  In  its 
passage  through  the  compact  bone  the  nutrient  artery  gives  off 
branches  to,  and  the  veins  receive  branches  from,  the  vessels  of  the 
Haversian  canals. 

Each  of  the  flat  and  of  the  short  bones  has  one  or  more  nutrient 
canals  for  the  transmission  of  the  nutrient  vessels. 

In  addition  to  the  nutrient  canals  the  surface  of  the  bone  is  every- 
where pierced  by  the  already  mentioned  (page  151)  Volkmann's 
canals,  which  serve  for  the  transmission  of  the  smaller  vessels.  In 
compact  bone  these  vessels  give  rise  to  a  network  of  branches  which 
run  in  the  Haversian  canals.  In  spongy  bone  the  network  lies  in 
the  marrow  spaces.  Branches  from  these  vessels  pass  to  the  marrow 
cavity,  and  there  break  up  into  a  capillary  network,  which  anasto- 
moses freely  with  the  capillaries  of  the  branches  of  the  nutrient 
artery. 

The  capillaries  of  marrow  empty  into  wide  veins  without  valves, 
the  walls  of  which  consist  of  a  single  layer  of  endothelium.  So  thin 
are  these  walls  that  the  veins  of  marrow  were  long  described  as 
passing  over  into  open  or  incompletely  walled  spaces  in  which  the 
blood  came  into  direct  contact  with  the  marrow  elements.  These 
veins  empty  into  larger  veins,  which  are  also  valveless.  Some  of 
these  converge  to  form  the  vein  or  veins  which  accompany  the  nu- 
trient artery ;  others  communicate  with  the  veins  of  the  Haversian 
canals. 

Lymphatics  with  distinct  walls  are  present  in  the  outer  layer  of 
the  periosteum.  Cleft-like  lymph  capillaries  lined  with  endothelium 
accompany  the  blood-vessels  in  Volkmann's  and  in  the  Haversian 
canals.  The  lacuna  and  canalicitli  constitute  a  complete  system  of 
lymph  channels  which  communicate  with  the  lymphatics  of  the 
periosteum,  of  Volkmann's  and  the  Haversian  canals,  and  of  the 
bone  marrow. 

Nerves. — Both  medullated  and  non-medullated  nerves  accompany 


156  THE  ORGANS. 

the  vessels  from  the  periosteum  through  Volkmann's  canals,  into  the 
Haversian  canals  and  marrow  cavities.  Pacinian  bodies  (page  350) 
occur  in  the  periosteum.  Of  nerve  endings  in  osseous  tissue  and  in 
marrow  little  definite  is  known. 

TECHNIC. 

(1)  Decalcified  Bone. — Fix  a  small  piece  of  the  shaft  of  one  of  the  long  bones 
— human  or  animal— in  formalin-Mullers  fluid  (technic  5,  p.  5),  and  decalcify  in 
hydrochloric  or  nitric-acid  Solution  (page  8).  After  decalcifying,  wash  until  all 
traces  of  acid  are  removed,  in  normal  saline  solution  to  which  a  little  ammonia  has 
been  added.  Dehydrate  and  embed  in  celloidin.  Transverse  and  longitudinal 
sections  are  made  through  the  shaft,  including  periosteum  and  edge  of  marrow 
cavity.  Stain  with  haematoxylin-eosin  (technic  1,  p.  16)  and  mount  in  eosin- 
glycerin. 

(2)  Hard  Bone. — Transverse  and  longitudinal  sections  of  undecalcified  bone 
may  be  prepared  as  in  technic  1,  p.  S3. 

(3)  Spongy  Bone. — This  may  be  studied  in  the  sections  of  decalcified  bone, 
technic  (1),  where  it  is  found  near  the  marrow  cavity.  Or  spongy  bone  from  the 
head  of  one  of  the  long  bones  or  from  the  centre  of  a  short  bone  may  be  prepared 
as  in  technic  (2). 

(4)  Red  Marrow. — Split  longitudinally  the  femur  of  a  child  or  young  animal, 
and  carefully  remove  the  cylinder  of  marrow.  Fix  in  formalin-Midler's  fluid  and 
harden  in  graded  alcohols.  Cut  sections  as  thin  as  possible,  stain  with  haema- 
toxylin-eosin, and  mount  in  balsam. 

(5)  Marrow — fresh  specimen.  By  means  of  forceps  or  a  vice,  squeeze  out  a 
drop  of  marrow  from  a  young  bone,  place  on  the  centre  of  a  mounting  slide,  cover 
and  examine  it  immediately. 

(6)  Place  a  similar  drop  of  marrow  on  a  cover-glass  and  cover  with  a  second 
cover-glass.  Press  the  covers  gently  together,  slide  apart  and  fix  the  specimen  by 
immersion  for  five  minutes  in  saturated  aqueous  solution  of  mercuric  chlorid. 
Wash  thoroughly,  stain  with  haematoxylin-eosin,  and  mount  in  balsam. 

Development  of  Bone. 

The  forms  of  bones  are  first  modelled  either  in  cartilage  or  in 
embryonic  connective  tissue.  The  bones  of  the  trunk,  extremities, 
and  parts  of  the  bones  of  the  base  of  the  skull  develop  in  a  matrix 
of  cartilage.  This  is  known  as  intracartilaginous  or  endochondral 
ossification.  The  flat  bones,  those  of  the  vault  of  the  cranium  and 
most  of  the  bones  of  the  face,  are  developed  in  a  matrix  of  fibrillar 
connective  tissue — intramembranous  ossification.  A  form  of  bone 
development,  similar  in  character  to  intramembranous,  occurs  in  con- 
nection with  both  intramembranous  ossification  and  intracartilaginous 
ossification.  This  consists  in  the  formation  of  bone  just  beneath  the 
perichondrium — subpcrichondrial   ossification — or,  as    with    the  de- 


THE  SKELETAL   SYSTEM. 


157 


velopment  of  bone  perichondrium  becomes  periosteum — subperiosteal 
ossification. 

There  are  thus  three  forms  of  bone  development  to  be  considered  : 
(1)  Intramembranous,  (2)  intracartilaginous,  and  (3)  subperiosteal. 

1.  Intramembranous  Development  (Fig.  92). — In  intramem- 
branous ossification  the  matrix  in  which  the  bone  is  developed  is 
connective  tissue.     The  process  of  bone  formation  begins  at  one  or 


FIG.  92.— Intramem'-iranous  Bone  Development.  Vertical  section  through  parietal  bone  of 
human  fcetus.  X  160.  (Technic  4,  p.  164.)  a.  Osteoblasts  ;  d,  bone  trabecular  ;  c,  osteo- 
clasts lying  in  Howship's  lacuna  ;  d,  internal  periosteum  ;  e,  bone  cells  ;  f,  calcified  fibres  ; 
g;  osteogenetic  tissue  ;  h,  external  periosteum  (pericranium). 


more  points  in  this  matrix.  These  are  known  as  ossification  centres. 
Here  some  of  the  bundles  of  white  fibres  become  calcified,  i.e.,  become 
impregnated  with  lime  salts.  There  is  thus  first  established  a  centre 
or  centres  of  calcification.  Between  the  bundles  of  calcified  fibres 
the  connective  tissue  is  rich  in  cells  and  vascular,  and  from  its  future 
role  in  bone  formation  is  known  as  osteogenetic  tissue  (Fig.  92). 
Along  the  surfaces  of  the  calcified  fibres  certain  of  the  osteogenetic 
cells  arrange  themselves  in  a  single  layer  (Figs.  92  and  93).  These 
are  now  known  as  osteoblasts  or  " bone  formers"  Under  the  influ- 
ence of  these  osteoblasts  a  thin  plate  of  bone  is  formed  between 


158  THE   ORGANS. 

themselves  and  the  calcified  fibres.  This  is  at  first  free  from  cells, 
but  as  the  lamella  of  bone  grows  in  thickness,  the  layer  of  osteoblasts 
becomes  completely  enclosed  by  bone.  The  osteoblasts  are  thus 
transformed  into  bone  cells  (Fig.  93),  the  spaces  in  which  they  lie 
becoming  bone  lacunce.  The  bone  cell  is  thus  seen  to  be  derived 
from  the  embryonic  connective-tissue  cell,  the  osteoblast  being  an 
intermediate  stage  in  its  development.  In  this  way  irregular  anas- 
tomosing trabecular  of  bone  are  formed  enclosing  spaces  (Fig.  92). 
The  bony  trabecular  at  first  contain  remains  of  calcified  connective- 
tissue  fibres,  while  the  spaces,  which  are  known  as  primary  narrow 
spaces,  contain  blood-vessels,  osteogenetic  tissue,  and  developing 
marrow.  The  osteoblasts  ultimately  disappear  and  the  spaces  are 
then  occupied  by  blood-vessels  and  marrow.  The  connective-tissue 
membrane  has  now  been  transformed  into  cancellous  or  spongy  bone 
(Fig.  86). 

The  bone  thus  formed  is  covered  on  its  outer  surface  by  a  layer 
of  connective  tissue,  a  part  of  the  membrane  in  which  the  bone  was 

a  b 


e  d  c 

Fig.  93.— Intramembranous  Bone  Development.  Vertical  section  through  parietal  bone  of 
human  foetus.  X  350.  (Technic  1,  p.  164.)  a,  Osteoblasts;  b,  calcined  fibres;  c,  osteoge- 
netic tissue  ;  d,  osteoclast  lying  in  Howship's  lacuna  ;  e,  bone  lacunae  ;  /,  bone. 

formed,  but  which  from  its  position  is  now  known  as  the  periosteum, 
or,  in  the  case  of  the  cranial  bones,  as  the  peri-  or  epicraniwn  (Fig. 
92). 

In  this  form  of  bone  development,  occurring  as  it  does  in  the 
bones  of  the  skull,  provision  must  be  made  for  increase  in  the  size  of 
the  cranial  cavity  to  accommodate  the  growing  brain.  This  is  ac- 
complished in  the  following  manner:  Along  the  surface  of  the  bone, 


THE  SKELETAL   SYSTEM. 


159 


directed  toward  the  brain,  large  multinuclear  cells — osteoclasts  or 
"bone  breakers" — make  their  appearance  (Fig.  93).  The  origin  of 
these  cells  is  not  clear.  Similar  cells  are  conspicuous  elements  of 
adult  marrow.  They  have  been  variously 
described  as  derived  from  leucocytes,  from 
osteoblasts,  or  directly  from  the  connective- 
tissue  cells.  A  recent  theory  holds  that 
they  are  derived  by  a  process  of  budding 
from  the  endothelial  cells,  which  form  the 
walls  of  the  capillaries.  These  osteoclasts 
by  a  process,  apparently  similar  to  solu- 
tion, break  down  the  bone  on  its  inner  sur- 
face, and  can  be  seen  lying  in  little  depres- 
sions-—  HowsJiip 's  lacuna  (Fig.  92) — which 
they  have  hollowed  out  in  the  bone.  Be- 
tween the  outer  surface  of  the  bone  and 
the  pericranium  is  a  layer  of  ostcogenetie 
tissue,  the  innermost  cells  of  which  are 
arranged  as  osteoblasts  along  the  outermost 
osseous  lamellae.  Here  they  are  constantly 
adding  new  bone  beneath  the  pericranium. 
This  new  bone  is  laid  down,  not  in  flat, 
evenly  disposed  layers,  but  in  the  form  of 
anastomosing  trabecular  enclosing  marrow 
spaces. 

It  is  thus  seen  that  subperiosteal  bone, 
like  intramembranous,  is  at  first  of  the 
spongy  variety,  and  that  with  the  develop- 
ment of  the  cranium  the  original  intra- 
membranous bone  is  entirely  absorbed,  to- 
gether with  much  of  the  subperiosteal. 

2.  Intracartilaginous  Development. — 
In  this  form  of  ossification  the  bones  are 
pre-formed  in    solid  embryonal  cartilages, 

which  correspond  more  or  less  closely  in  shape  to  the  future  bones 
(Fig.  94).  Covering  the  surface  of  the  cartilage  is  a  membrane  of 
fibrillar  connective  tissue,  the  perichondrium  or  primary  peri- 
osteum. 

In  most  of  the  long  bones  the  earliest  changes  take  place  within 


FIG.  94. — Intracartilaginous  Bone 
Development.  Longitudinal 
section  of  one  of  the  bones  of 
embryo  sheep's  foot,  showing 
ossification  centre.  X  20. 
(Technic  2,  p.  164.)  <?,  Perios- 
teum ;  b,  blood-vessels  ;  c. 
subperiosteal  bone  ;  </,  intra- 
cartilaginous bone  ;  e,  osteo- 
genetic  tissue  ;  f.  cartilage  ; 
£-,  ossification  centre  ;  //,  calci- 
fication zone. 


i6o 


THE   ORGANS. 


^,« 


'       - 


the  cartilage  at  about  the  centre  of  the  shaft  (Fig.  94).  Here  the 
cartilage  cells  increase  in  size  and  in  number  in  such  a  way  that 
several  enlarged  cartilage  cells  come  to  lie  in  a  single  enlarged  cell 
space.     The  cartilage  thus  assumes  the  character  of  hyaline  carti- 

a  lagc.     The  cell  groups  next  ar- 

range themselves  in  rows  or  col- 
umns, which  at  first  extend 
outward  in  a  radial  manner 
from  a  common  centre,  but 
later  lie  in  the  long  axis  of  the 
bone.  During  these  changes 
in  the  cells  there  is  an  increase 
in  the  intercellular  matrix  and 
a  deposit  there  of  calcium  salts. 
In  this  way  the  cartilage  be- 
comes calcified,  the  area  in- 
volved being  known  as  the 
calcification  centre.  Further 
growth  of  cartilage  at  the  cal- 
cification centre  now  ceases 
and,  as  growth  of  cartilage  at 
the  ends  of  the  bone  continues, 
the  central  portion  of  the 
shaft  appears  constricted.  The 
changes  up  to  this  point  seem 
to  be  preparatory  to  actual 
bone  formation. 

Ossification  proper  begins  by  blood-vessels  from  the  periosteum  1 
pushing  their  way  into  the  calcified  cartilage  at  the  calcification  cen- 
tre, carrying  with  them  some  of  the  osteogenetic  tissue  from  beneath 
the  periosteum.  These  blood-vessels  with  their  accompanying  osteo- 
genetic tissue  are  known  as  periosteal  buds  (Fig.  95).  Osteoblasts 
now  develop  from  the  osteogenetic  tissue  and  appear  to  dissolve  the 
calcified  cartilage  from  in  front  of  the  advancing  vessels.  In  this 
way  the  septa  between  the  cartilage  cell  spaces  are  broken  down,  the 
cartilage  cells  disappear,  and  a  central  cavity  is  formed — the  primary 

'The  term  "periosteum  "  is  admissible  from  the  fact  that  the  first  bone  act- 
ually formed  is  beneath  the  perichondrium,  which  thus  becomes  converted  into 
periosteum. 


FlG.  95. — Intracartilaginous  Bone  Develop- 
ment. X  350.  Showing  osteogenetic  tissue 
pushing  its  way  into  the  cartilage  (perios- 
teal bud)  at  the  ossification  centre,  a,  Peri- 
osteum ;  fi,  cartilage  cell  spaces  ;  c,  perios- 
teal bud  ;  </,  blood-vessel  ;  e,  cartilage  cells  ; 
f,  cartilage  matrix. 


THE  SKELETAL   SYSTEM. 


161 


marrow  cavity.  From  the  region  of  the  primary  marrow  cavity 
blood-vessels  and  osteogenetic  tissue  push  in  both  directions  toward 
the  ends  of  the  cartilage  which  is  to  be  replaced  by  bone.  These 
break  down  the  transverse  septa  between  the  cell  spaces,  while  many 
of  the  longitudinal  septa  at  first  remain  to  form  the  walls  of  long  anas- 
tomosing channels,  the  primary  marrow  spaces  (Fig.  96).  As  in  intra- 
membranous  bone,  these  contain  blood-vessels,  embryonal  marrow, 
and  osteoblasts,  all  of  which  are  derived  from  the  osteogenetic  tissue 
brought  in  from  the  periosteum  by  the  periosteal  buds.  The  osteo- 
blasts next  arrange  themselves  in  a  single  layer  along  the  remains  of 
the  calcified  cartilage,  where  they  proceed  to  deposit  a  thin  layer  of 
bone  between  themselves  and  the  cartilage  (Fig.  97).  As  this 
increases  in  thickness  some  of  the  osteoblasts  are  enclosed  within 
the  newly  formed  bone  to  become  bone  cells,  while  the  remains  of  the 
cartilage  diminish  in  amount  and  finally  disappear.  The  calcifi- 
cation centre  has  now  become  the  ossification  centre,  and  its  anasto- 
mosing osseous  trabecular,  with  a 
their  enclosed  spaces  containing 
osteogenetic  tissue  and  marrow, 
constitute  primary  spongy  bone. 
At  either  end  of  the  ossifi- 
cation centre  the  cartilage  pre- 
sents a  special  structure.  Near- 
est the  centre  the  cell  spaces 
are  enlarged,  flattened,  arranged 
in  rows,  and  contain  shrunken 
cells.  Some  of  the  walls  break 
down  and  irregular  spaces  are 
formed.  The  ground  substance 
is  calcified.  Passing  away  from 
the  ossification  centre,  the  cell 
spaces  become  less  flattened, 
still  arranged  in  rows,  the  con- 
tained cells  larger,  and  there  is 
a  lesser  degree  of  calcification. 
This  area  passes  over  into  an 
area  of  hyaline  cartilage  which  blends  without  distinct  demarcation 
with  the  ordinary  embryonal  cartilage  of  the  rest  of  the  shaft.      The 

area  of  calcified  cartilage  at  either  end  of  the  ossification  centre  is 
1 1 


FIG.  96. — Intracartilaginous  Bone  Development. 
Same  specimen  as  Fig-.  94  (x  350),  showing  os- 
teogenetic tissue  pushing  its  way  into  the  car- 
tilage and  breaking  it  up  into  trabecular  ;  also 
formation  of  primary  marrow  spaces  and  dis- 
integration of  cartilage  cells,  a.  Disintegrating 
cartilage  cells  ;  />,  cartilage  trabecula  ;  c,  osteo- 
genetic tissue  in  primary  marrow  space  ;  d, 
blood-vessel  ;  e,  cell  spaces  ;  f,  cartilage  cells. 


1 62 


THE  ORGANS. 


known  as   the  calcification  zone  and  everywhere  precedes  the  forma- 
tion of  true  bone  (Fig.  94). 

3.  Subperiosteal  or  subperichondrial  development  (Fig.  94) 
has  already  been  largely  described  in  connection  with  intramem- 
branous  ossification,  and  differs  in  no  important  respect  from  the 
latter.  It  always  accompanies  one  of  the  other  forms  of  ossification. 
Bone  appears  beneath  the  perichondrium  somewhat  earlier  than 
within  the  underlying  cartilage.  Beneath  the  perichondrium  is  a 
layer  of  rich  cellular  osteogenetic  tissue.     The  cells  of  this  tissue 


FIG.  97. — Intracartilaginous  Bone  Development.  Same  specimen  as  Fig.  94  (X  350),  showing 
bone  being  deposited  around  one  of  the  trabeculse  of  cartilage,  a,  Blood-vessel  ;  b.  bone  ; 
c,  cartilage  remains  ;  d.  bone  cell  ;  e,  cartilage  cell  space;  f,  osteoblasts  ;  g;  osteogenetic 
tissue  ;  /i,  lamella  of  bone  ;  i,  connective-tissue  cells  ;  /,  cartilage  cell. 

nearest  the  cartilage  become  osteoblasts  and  arrange  themselves  in  a 
single  layer  along  its  surface.  Under  their  influence  bone  is  laid 
down  on  the  surface  of  the  cartilage  in  the  same  manner  as  in  intra- 
membranous  ossification. 

Intracartilaginous  and  subperiosteal  bone  can  be  easily  differen- 
tiated by  the  presence  of  cartilaginous  remains  in  the  former  and 
their  absence  in  the  latter. 


All  bone  is  at  first  of  the  spongy  variety.  When  this  is  to  be 
converted  into  compact  bone,  there  is  first  absorption  of  bone  by 
osteoclasts,  with  increase  in  size  of  the  marrow  spaces  and  reduction 
of  their  walls  to  thin  plates.  These  spaces  are  now  known  as  Haver- 
sian spaces.  Within  these  new  bone  is  deposited.  This  is  done  by 
osteoblasts  which  lay  down  layer  within  layer  of  bone  until  the 
Haversian  space  is  reduced  to  a  mere  channel,  the  Haversian  canal. 


THE  SKELETAL   SYSTEM.  163 

In  this  way  are  formed  the  Haversian  canals  and  the  Haversian  sys- 
tems of  lame  lice.  Some  of  the  interstitial  lamellae  are  the  remains  of 
the  original  spongy  bone  not  quite  removed  in  the  enlargement  of 
the  primary  marrow  spaces  to  form  the  Haversian  spaces  ;  other  in- 
terstitial lamellae  appear  to  be  early  formed  Haversian  lamellae  which 
have  been  more  or  less  replaced  by  Haversian  lamellae  formed  later. 

While  these  varieties  of  ossification  have  been  described,  we 
would  emphasize  the  essential  unity  of  the  process.  The  likeness 
between  intramembranous  and  subperiosteal  ossification  has  been 
already  noted.  The  differences  observed  in  intracartilaginous  ossi- 
fication are  more  apparent  than  real.  In  intracartilaginous  ossifica- 
tion the  bone  is  developed  in  cartilage  but  not  from  cartilage.  As  in 
intramembranous  and  in  subperiosteal  ossification,  intracartilaginous 
bone  is  developed  from  osteogenetic  tissue.  This  osteogenetic  tissue 
is  a  differentiation  of  embryonal  connective  tissue,  in  this  case  car- 
ried into  the  cartilage  from  the  periosteum  in  the  periosteal  buds. 
In  intramembranous  ossification  the  bone  is  developed  within  and 
directly  from  the  embryonal  connective  tissue  of  which  the  mem- 
brane is  composed.  In  intracartilaginous  ossification  there  is  the 
same  embryonal  connective-tissue  membrane,  but  within  this  mem- 
brane the  form  of  the  bone  is  first  laid  down  in  embryonal  cartilage. 
Surrounding  the  cartilage  there  remains  the  embryonal  connective 
tissue  of  the  membrane,  now  perichondrium.  It  is  from  tissue  which 
grows  into  the  cartilage  from  this  membrane — embryonal  connective 
tissue — that  the  bone,  although  developed  in  cartilage,  is  formed. 

Growth  of  Bone. 

The  growth  of  intramembranous  bone  by  the  formation  of  succes- 
sive layers  beneath  the  periosteum  has  been  already  described  (page 

159)- 

Intracartilaginous  bones  grow  both  in  diameter  and  in  length. 

Grozvth  in  diameter  is  accomplished  by  the  constant  deposition 
of  new  layers  of  bone  beneath  the  periosteum.  During  this  process, 
absorption  of  bone  from  within  by  means  of  osteoclasts  leads  to  the 
formation  of  the  marrow  cavity.  The  hard  bone  of  the  shaft  of  a 
long  bone  is  entirely  of  subperiosteal  origin,  the  intracartilaginous 
bone  being  completely  absorbed. 


1 64  THE   ORGANS. 

Growth  in  length  takes  place  in  the  following  manner:  Some 
time  after  the  beginning  of  ossification  in  the  shaft  or  diaphysis,  in- 
dependent ossification  centres  appear  in  the  ends  of  the  bone  (epiph- 
yses). So  long  as  bone  is  growing,  the  epiphyses  and  diaphysis 
remain  distinct.  Between  them  lies  a  zone  of  growing  cartilage,  the 
epiphyseal  or  intermediate  cartilage.  Increase  in  length  of  the  bone 
takes  place  by  a  constant  extension  of  ossification  into  this  cartilage 
from  the  ossification  centres  of  the  epiphyses  and  diaphysis.  After 
the  bone  ceases  to  grow  in  length,  the  epiphyses  and  diaphysis 
become  firmly  united. 

ECHNIC. 

(i)  Developing  Bone  —  Intramembranous. — Small  pieces  are  removed  from  near 
the  edge  of  the  parietal  bone  of  a  new-born  child  or  animal.  These  pieces  should 
include  the  entire  thickness  of  bone  with  the  attached  scalp  and  dura  mater. 
Treat  as  in  technic  i,  p.  156,  except  that  the  sections  which  are  cut  perpendicular 
to  the  surface  of  the  bone  should  be  stained  with  haematoxylin-picro-acid-fuchsin 
(technic  3,  p.  16)  and  mounted  in  balsam. 

(2)  Developing  Bone — Intracartilaginous  and  Subperiosteal. — Remove  the 
forearms  and  legs  of  a  human  or  animal  embryo  by  cutting  through  the  elbow  and 
knee-joints.  (Foetal  pigs  from  five  to  six  inches  long  are  very  satisfactory.)  Treat 
as  in  technic  (1).  Block  so  that  the  two  long  bones  will  lie  in  such  a  plane  that 
both  will  be  cut  at  the  same  time.  Cut  thin  longitudinal  sections  through  the  ossi- 
fication centres,  stain  with  hamiatoxylin-picro-acid-fuchsin,  and  mount  in  balsam. 
Cut  away  the  ends  of  one  or  two  of  the  embedded  bones,  leaving  only  the  ossifica- 
tion centres.  Block  so  as  to  cut  transverse  sections  through  the  ossification  centre. 
Stain  and  mount  as  the  preceding. 

In  the  picro-acid-fuchsin  stained  sections  of  developing  bone  the  cartilage  is 
stained  blue:  cells,  including  red  blood  cells,  yellow;  connective  tissue  from  pale 
pink  to  red,  according  to  density;  bone  a  deep  red. 

The    Cartilages. 

The  costal  cartilages  are  hyaline.  They  are  covered  by  a  closely 
adherent  connective-tissue  membrane,  the  perichondrium.  Where 
cartilage  joins  bone  tbere  is  a  firm  union  between  the  two  tissues 
and  the  perichondrium  becomes  continuous  with  the  periosteum. 

The  articular  cartilages  are  described  below  under  articulations. 

The  other  skeletal  cartilages,  such  as  those  of  the  larynx,  trachea, 
bronchi,  and  of  the  organs  of  special  sense,  are  more  conveniently 
considered  with  the  organs  in  which  they  occur. 


THE  SKELETAL   SYSTEM.  165 

Articulations. 

Joints  are  immovable  (synarthrosis)  or  movable  (diarthrosis).  In 
synarthrosis  union  maybe  cartilaginous  (synchondrosis),  or  by  means 
of  fibrous  connective  tissue  (syndesmosis). 

Synchondrosis. — The  cartilage  is  usually  of  the  fibrous  form 
except  near  the  edge  of  the  bone,  where  it  is  hyaline.  The  interver- 
tebral discs  consist  of  a  ring  of  fibro-cartilage  surrounding  a  central 
gelatinous  substance,  the  nucleus  pulposus,  the  latter  representing 
the  remains  of  the  notochord. 

Syndesmosis. — Union  is  by  means  of  ligaments.  These  may 
consist  wholly  of  fibrous  tissue,  the  fibres  and  cells  being  arranged 
much  as  in  tendon,  or  mainly  of  coarse  elastic  fibres  separated  by 
loose  fibrous  tissue.  In  such  syndesmoses  as  the  sutures  of  the 
cranial  bones,  the  union  is  by  means  of  short  fibrous  ligaments 
between  the  adjacent  serrated  edges. 

Diarthrosis. — In  diarthrosis  must  be  considered  (a)  the  articular 
cartilages,  (/;)  the  glenoid  ligaments  and  interarticular  cartilages,  (c) 
the  joint  capsule. 

(a)  Articular  cartilages  cover  the  ends  of  the  bones.  They  are 
of  the  hyaline  variety,1  being  the  remains  of  the  original  cartilaginous 
matrix  in  which  the  bones  are  formed.  Next  to  the  bone  is  a  narrow 
strip  of  cartilage  in  which  the  matrix  is  calcified.  This  is  separated 
from  the  remaining  uncalcified  portion  of  the  cartilage  by  a  narrow 
so-called  "striated"  zone.  The  most  superficial  of  the  cartilage 
cells  are  arranged  in  rows  parallel  to  the  surface;  in  the  mid-region 
the  grouping  of  cells  is  largely  in  twos  and  fours  as  in  ordinary 
hyaline  cartilage  (page  80) ;  while  in  the  deepest  zone  of  the  uncal- 
cified cartilage  the  cells  are  arranged  in  rows  perpendicular  to  the 
surface. 

(b)  The  glenoid  ligaments  and  interarticular  cartilages  conform 
more  to  the  structure  of  dense  fibrous  tissue  than  to  that  of  cartilage. 

(c)  The  joint  capsule  consists  of  two  layers,  an  outer  layer  of 
dense  fibrous  tissue  intimately  blended  with  the  ligamentous  struc- 
tures of  the  joint  and  known  as  the  stratum  fibrosum,  and  an  inner 

!  In  the  acromioclavicular,  sternoclavicular,  costo-vertebral,  and  maxillary 
articulations  the  cartilage  is  of  the  fibrous  form.  The  same  is  true  of  the  carti- 
lage covering  the  head  of  the  ulna,  while  the  surface  of  the  radius,  which  enters 
into  the  wrist-joint,  is  covered  not  by  cartilage,  but  by  dense  fibrous  tissue. 


1 66  THE   ORGANS. 

layer,  the  stratum  synoviale  or  synovial  membrane,  which  forms  the 
lining  of  the  joint  cavity.  The  outer  part  of  the  stratum  synoviale 
consists  of  areolar  tissue  with  its  loosely  arranged  white  and  elastic 
fibres  interlacing  in  all  directions  and  scattered  connective-tissue 
cells  and  fat  cells.  Nearer  the  free  surface  of'  the  membrane  the 
fibres  run  parallel  to  the  surface  and  the  cellular  elements  are  more 
abundant.  The  cells  are  scattered  among  the  fibres  and  are  stel- 
late branching  cells  like  those  usually  found  in  fibrous  connective 
tissue.  On  the  free  surface,  however,  the  cells  are  closely  packed 
and  although  in  places  often  several  layers  deep,  are  probably  of  the 
nature  of  endothelium. 

From  the  free  surfaces  of  synovial  membranes  processes  {synovial 
villi — Haversian  fringes)  project  into  the  joint  cavity.  Some  of 
these  are  non-vascular  and  consist  mainly  of  stellate  cells  similar  to 
those  of  the  synovial  membrane.  Others  have  a  distinct  core  of 
fibrous  tissue  containing  blood-vessels  and  covered  with  stellate  con- 
nective-tissue cells.  From  the  primary  villi  small  secondary  non- 
vascular villi  are  frequently  given  off. 

TECHNIC. 

(i)  Joint  Capsule  and  Articular  Cartilage. — Remove  one  of  the  small  joints — 
human  or  animal — cutting  the  bones  through  about  one-half  inch  back  from  the 
joint.  Treat  as  in  technic  i.  p.  156,  making  longitudinal  sections  through  the  en- 
tire joint. 

(2)  Synovial  Villi. — Remove  a  piece  of  the  capsular  ligament  from  near  the 
border  of  the  patella  and  cut  out  a  bit  of  the  velvety  tissue  which  lines  its  inner 
surface.  Examine  fresh  in  a  drop  of  normal  salt  solution.  Fix  a  second  piece  of 
the  ligament  in  formalin-Miiller's  fluid  (technic  5,  p.  5),  make  sections  perpen- 
dicular to  the  surface,  stain  with  ha.matoxylin-eosin  (technic  1,  p.  16),  and  mount 
in  balsam. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre,  vol.  i. 
Stohr:  Text-book  of  Histology. 

Schafer:  Histology  and  Microscopical  Anatomy,  in  Quain's  Elements  of 
Anatomy. 


CHAPTER    IV. 
THE    MUSCULAR    SYSTEM.1 

The  voluntary  muscular  system  consists  of  a  number  of  organs — 
the  muscles — and  of  certain  accessory  structures — the  tendons,  tendon 
sheaths,  and  bursa. 

A  voluntary  muscle  consists  of  striated  muscle  fibres  arranged 
in  bundles  or  fascicles  and  supported  by  connective  tissue. 

The  entire  muscle  is  enclosed  by  a  rather  firm  connective-tissue 
sheath  or  capsule — the  cpimysium  (Fig.  98).      This  sends  trabecular 


FlG.  98. — From  a  Transverse  Section  of  a  Small  Human  Muscle,  showing  relations  of  muscle 
fibres  to  connective  tissue,  a,  Epimysium  ;  6,  perimysium;  c,  muscle  fibres;  d,  arteries; 
e,  endomysium. 

of  somewhat  more  loosely  arranged  connective  tissue  into  the  sub- 
stance of  the  muscle.  These  divide  the  muscle  fibres  into  fascicles. 
Around  each  fascicle  the   connective  tissue   forms   a  more  or   less 


1  Definite  arrangements  of  smooth  muscle,  such  as  are  found  in  the  stomach 
and  intestines,  also  the  muscle  of  the  heart  are  properly  a  part  of  the  muscular  sys- 
tem. They  are,  however,  best  considered  under  tissues  and  in  connection  with  the 
organs  in  which  they  occur. 

167 


i68 


THE   ORGANS. 


;77, .  ;     '■  fowl 

>.  V,''/ 

>  liA  V! 

iV.n  i',vV>'.3 


'     ' '  i   '  ,',-,  V,", 


^  till 


definite  envelope,  the  per  {fascicular  sheath  or  perimysium.  From 
the  latter  delicate  strands  of  connective  tissue  pass  into  the  fascicles 
between  the  individual  muscle  fibres.  This  constitutes  the  intrafas- 
cicular  connective  tissue  or  endomysium,  which  everywhere  completely 
separates  the  fibres  from  one  another  so  that  the  sarcolemma  of  one 
fibre  never  comes  in  contact  with  the  sarcolemma  of  any  other  fibre. 
It  should  be   noted  that  these  terms   indicate  merely  location;  epi-, 

peri-,  and  endomysium  all  being 
connective  tissue  grading  from 
coarse  to  fine,  as  it  passes  from 
without  inward.  The  structure 
of  the  muscle  as  an  organ  is 
thus  seen  to  conform  to  the 
structure  of  other  organs,  in 
that  it  is  surrounded  by  a  con- 
nective-tissue capsule,  which 
sends  septa  into  the  organ,  divid- 
ing it  into  a  number  of  com- 
partments and  serving  for  the 
support  of  the  essential  tissue 
of  the  organ,  the  muscle  fibres 
or  parenchyma. 

The  structure  of  tendon  has 
been  described  (see  page  67). 

Tendon  slieatJis  and  burses 
are  similar  in  structure,  consist- 
ing of  mixed  white  and  elastic 
fibres.  Their  free  surfaces  are 
usually  lined  by  flat  cells,  which  are  described  by  some  as  connec- 
tive-tissue cells,  by  others  as  endothelium. 

At  the  junction  of  muscle  and  tendon,  the  muscle  fibre  with  its 
sarcolemma  ends  in  a  rounded  or  blunt  extremity  (Fig.  54,  p.  96). 
Here  the  fibrils  of  the  tendon  fibres  are  in  part  cemented  to  the  sar- 
colemma, and  in  part  are  continuous  with  the  fibres  of  the  endo-  and 
perimysium.  Along  the  line  of  union  of  muscle  and  tendon  the 
muscle  nuclei  are  more  numerous  than  elsewhere  (Fig.  99,  b),  and  it 
has  been  suggested  that  there  is  here  a  zone  of  indifferent  or  forma- 
tive tissue  which  is  capable  of  developing  on  the  one  hand  into  mus- 
cle, on  the  other  into  the  connective  tissue  of  tendon. 


■    /       rli    /  (<  1    ■■>    '/i    'luff      ,    •  «  •  'i 

Y^^r^ri-    -)  1    i      it  m  ■■. ..;  .; 


i 


t 


* 


Fig.  99. — From  a  Longitudinal  Section  through 
Junction  of  Muscleand  Tendon.  X150.  (Bohm 
and  Davidoff.)  a,  Tendon  ;  b,  line  of  union 
showing  increase  in  number  of  muscle  nuclei; 
c,  muscle. 


THE  MUSCULAR   SYSTEM.  169 

Growth  of  muscle  takes  place  mainly  at  the  ends  of  the  fibres 
where  the  nuclei  are  most  numerous.  In  addition  to  the  growth 
incident  to  increase  in  size  of  the  individual  or  of  the  particular  mus- 
cle, there  is  a  constant  wearing  out  of  muscle  fibres  and  their 
replacement  by  new  fibres.  This  is  accomplished  as  follows  :  The 
muscle  fibre  first  breaks  up  into  a  number  of  segments  (sarcostyles), 
some  of  which  contain  nuclei  while  others  are  non-nucleated.  The 
sarcostyles  next  divide  into  smaller  fragments,  and  finally  completely 
disintegrate.  This  is  followed  by  a  process  of  absorption  and  complete 
disappearance  of  the  fibre.  From  the  free  sarcoplasm  new  muscle 
fibres  are  formed.  In  the  early  stages  of  their  development  these  are 
known  as  myoblasts.  The  latter  develop  into  muscle  fibres  in  the 
same  manner  as  described  under  the  histogenesis  of  muscle  (page  99). 

Blood-vessels. — The  larger  arteries  of  muscle  run  in  the  perimy- 
sium, their  general  direction  being  parallel  to  the  muscle  bundles. 
From  these,  small  branches  are  given  off  at  right  angles.  These  in 
turn  give  rise  to  an  anastomosing  capillary  network  with  elongated 
meshes,  which  surrounds  the  individual  muscle  fibres  on  all  sides. 
From  these  capillaries,  veins  arise  which  follow  the  arteries.  Even 
the  smallest  branches  of  these  veins  are  supplied  with  valves. 

In  tendons  blood-vessels  are  few.  They  run  mainly  in  the  con- 
nective tissue  which  surrounds  the  fibre  bundles.  Tendon  sheaths 
and  bursae,  on  the  other  hand,  are  well  supplied  with  blood-vessels. 

The  lymphatics  of  muscle  are  not  numerous.  They  accompany 
the  blood-vessels.  In  tendon  definite  lymph  vessels  are  found  only 
on  the  surface. 

Nerves. — The  terminations  of  nerves  in  muscle  and  tendon  are 
described  under  nerve  endings  (page  350). 

TECHNIC. 

(1)  A  Muscle.— Select  a  small  muscle,  human  or  animal,  and,  attaching  a  weight 
to  the  lower  end  to  keep  it  stretched,  fix  in  formalin-Midler's  fluid  (technic  5,  p.  5), 
and  harden  in  alcohol.  Stain  transverse  sections  with  haematoxylin-picro-acid- 
fuchsin  (technic  3,  p.  16)  and  mount  in  balsam. 

(2)  Junction  of  Muscle  and  Tendon. — Any  muscle-tendon  junction  may  be 
selected.  Fix  in  formalin-Muller's  fluid,  keeping  stretched  by  means  of  a  weight 
attached  to  the  lower  end.  Cut  longitudinal  sections  through  the  muscle-tendon 
junction,  stain  with  haematoxylin-picro-acid-fuchsin,  and  mount  in  balsam.  The 
gastrocnemius  of  a  frog  is  convenient  on  account  of  its  small  size,  and  because  by 
bending  the  knee  over  and  tying  there,  the  muscle  can  be  easily  put  on  the  stretch 
and  kept  in  that  condition  during  fixation.  Place  the  entire  preparation  in  the 
fixative,  removing  the  muscle-tendon  from  the  bone  after  fixation. 


CHAPTER    V. 

GLANDS   AND    THE    GENERAL   STRUCTURE   OF 
MUCOUS    MEMBRANES. 

Glands — General  Structure  and  Classification. 

Attention  was  called  in  describing  the  functional  activities  of 
cells  (page  37)  to  the  fact  that  certain  cells  possess  the  power  of 
not  only  carrying  on  the  nutritive  functions  necessary  to  the  main- 
tenance of  their  own  existence,  but  also  of  elaborating  certain  prod- 
ucts either  necessary  to  the  general  body  functions  (secretions),  or 
necessary  that  the  body  should  eliminate  as  waste  (excretions). 
Such  cells  are  known  as  gland  cells  or  glandular  epithelium,  and 
their  association  to  form  a  definite  structure  for  the  purpose  of  carry- 
ing on  secretion  or  excretion  is  known  as  a  gland. 

A  gland  may  consist  of  a  single  cell,  as,  e.g. ,  the  mucous  or  gob- 
let cell  on  the  free  surface  of  a  mucous  membrane.  Such  a  cell 
undergoes  certain  changes  by  which  a  portion  of  its  protoplasm  is 
transformed  into  or  replaced  by  a  substance  which  is  to  be  used  out- 
side the  cell  in  which  it  is  elaborated.  When  fully  developed  the 
cell  surface  ruptures  and  the  secretion  is  poured  out  upon  the  free 
surface. 

Most  glands  are,  however,  composed  of  more  than  one  cell,  usu- 
ally of  a  large  number  of  cells,  and  these  cells,  instead  of  lying 
directly  upon  the  surface,  line  more  or  less  extensive  invaginations 
into  which  they  pour  their  secretions. 

In  the  simplest  form  of  glandular  invagination  all  of  the  cells 
lining  the  lumen  are  secreting  cells.  In  more  highly  developed 
glands  only  the  deeper  cells  secrete,  the  remainder  of  the  gland 
serving  merely  to  carry  the  secretion  to  the  surface.  This  latter 
part  is  then  known  as  the  excretory  duct,  in  contradistinction  to  the 
deeper  secreting  portion.  In  both  the  duct  portion  and  secretory 
portion  of  a  gland  the  epithelium  usually  rests  upon  a  more  or  less 
definite  basement  membrane  or  membrana  propria  (page  53).  Be- 
neath the  basement  membrane,  separating  and  supporting  the  glandu- 

170 


GLANDS  AND  MUCOUS  MEMBRANES.  i/i 

lar  elements,  is  the  connective  tissue  of  the  gland.  This  varies 
greatly  in  structure  and  quantity  in  different  glands. 

When  the  secreting  portion  of  the  gland  is  a  tubule  the  lumen 
of  which  is  of  fairly  uniform  diameter,  the  gland  is  known  as  a  tubu- 
lar gland.  When  the  lumen  of  the  secreting  portion  is  dilated  in 
the  form  of  a  sac  or  alveolus,  the  gland  is  known  as  a  saccular  or 
alveolar  gland. 

A  gland  may  consist  of  a  single  tubule  or  saccule,  or  of  a  single 
system  of  ducts  leading  to  terminal  tubules  or  saccules — simple 
gland.  A  gland  may  consist  of  a  number  of  more  or  less  elaborate 
duct  systems  with  their  terminal  tubules  or  saccules — compound 
gland. 

All  compound  glands  are  surrounded  by  connective  tissue  which 
forms  a  more  or  less  definite  capsule.  From  the  capsule  connective- 
tissue  septa  or  trabecules  extend  into  the  gland.  The  broadest  septa 
usually  divide  the  gland  into  a  number  of  macroscopic  compartments 
or  lobes.  Smaller  septa  from  the  capsule  and  from  the  interlobular 
septa  divide  the  lobes  into  smaller  compartments  usually  microscopic 
in  size — the  lobules.  A  lobule  is  not  only  a  definite  portion  of  the 
gland  separated  from  the  rest  of  the  gland  by  connective  tissue,  but 
represents  a  definite  grouping  of  tubules  or  alveoli  with  reference  to 
one  or  more  terminal  ducts.  The  glandular  tissue  is  known  as  the 
parenchyma  of  the  gland,  in  contradistinction  to  the  connective  or 
interstitial  tissue. 

Glands  may  thus  be  classified  according  to  their  shape  and  ar- 
rangement as  follows  : 

1.  Tubular  glands. 

f  straight, 
i 

(a)  Simple  tubular     -J  coiled. 

[_  branched. 

(b)  Compound  tubular. 

2.  Saccular  or  alveolar. 

(a)  Simple  saccular. 

(b)  Compound  saccular  or  racemose. 

I.  Tubular  Glands. — (a)  Simple  tubular  glands  are  simple 
tubules  which  open  on  the  surface,  their  lining  epithelium  being  con- 
tinuous with  the  surface  epithelium.  All  of  the  cells  may  be  secret- 
ing cells  or  only  the  more  deeply  situated.  In  the  latter  case  the 
upper  portion  of  the  tubule  serves  merely  as  a  duct.     In  the  more 


v^ 


THE   ORGANS. 


highly  developed  of  the  simple  tubular  glands  we  distinguish  a 
month,  opening  upon  the  surface,  a  neck,  usually  somewhat  con- 
stricted, and  ■&  fundus,  or  deep  secreting  portion  of  the  gland. 

Simple  tubular  glands  are  divided  according  to  the  behavior  of 
the  fundus,  into  (i)  straight,  (2)  coiled,  and  (3)  branched. 

(1)  A  straight  tubular  gland  is  one  in  which  the  entire  tubule 
runs  a  straight  unbranched  course,  e.g.,  the  glands  of  the  large  intes- 
tine (Fig.  100,  /). 

(2)  A  coiled  tubular  gland  \s>  one  in  which  the  deeper  portion  of 
the  tubule  is  coiled  or  convoluted,  e.g. ,  the  sudoriferous  glands  of  the 
skin  (Fig.  100,  2). 

(3)  Forked  or  branched  tubular  glands  are  simple  tubular  glands 
in   which   the   deeper   portion   of    the   tubule   branches,  the   several 


6 


fa 


FIG.  100. — Diagram  Illustrating  Different  Forms  of  Glands.  Upper  row,  tubular  glands  ;  /,  2, 
and  j,  simple  tubular  glands  ;  ./,  compound  tubular  gland.  Lower  row,  alveolar  glands  ; 
/  a,  2<7,  and  ja,  simple  alveolar  glands  ;  ./a,  compound  alveolar  gland.  For  description  of 
/  u,  sa,  and  j  a,  see  simple  alveolar  glands  in  text. 


branches  being  lined  with  secreting  cells  and  opening  into  a  super- 
ficial portion,  which  serves  as  a  duct.  Examples  of  slightly  forked 
glands  are  seen  in  the  cardiac  end  of  the  stomach  and  in  the  uterus. 
Other  tubular  glands  show  much  more  extensive  branching.  The 
main  duct  gives  rise  to  a  number  of  secondary  ducts,  from  which  are 
given  off  the  terminal   tubules.     The  mucous   glands  of  the  mouth, 


GLANDS  AND  MUCOUS  MEMBRANES.  173 

oesophagus,  trachea,  and  bronchi  are  examples  of  these  more  elabo- 
rate simple  tubular  glands. 

(/?)  Compound  tubular  glands  consist  of  a  number,  often  of  a 
large  number,  of  distinct  duct  systems.  These  open  into  a  common 
or  main  excretory  duct.  The  smaller  ducts  end  in  terminal  tubules. 
Many  of  the  largest  glands  of  the  body  are  of  this  type,  e.g. ,  the 
salivary  glands,  liver,  kidney,  testis. 

In  certain  compound  tubular  glands,  as,  e.g.,  the  liver,  extensive 
anastomoses  occur  between  the  terminal  tubules.  These  are  some- 
times called  reticular  glands. 

2.  Alveolar  Glands. — (a)  Simple  Alveolar  Glands. — The 
simplest  form  of  alveolar  gland  consists  of  a  single  sac  connected 
with  the  surface  by  a  constricted  portion,  the  neck,  the  whole  being 
shaped  like  a  flask  (Fig.  100,  Id).  Such  glands  are  found  in  the 
skin  of  certain  amphibians ;  they  do  not  occur  in  man.  Simple 
alveolar  glands,  in  which  there  are  several  saccules  (Fig.  100,  2a), 
are  represented  by  the  smaller  sebaceous  glands.  Simple  branched 
alveolar  glands,  in  which  a  common  duct  gives  rise  to  a  number  of 
saccules  (Fig.  ioo,  Ja),  are  seen  in  the  larger  sebaceous  glands  and 
in  the  Meibomian  glands. 

(/;)  Compound  Alveolar  Glands. — These  resemble  the  com- 
pound tubular  glands  in  general  structure,  consisting  of  a  large  num- 
ber of  duct  systems,  all  emptying  into  a  common  excretory  duct.  The 
main  duct  of  each  system  repeatedly  branches,  and  the  small  terminal 
ducts,  instead  of  ending  in  blind  tubules,  as  in  the  compound  tubular 
gland,  end  in  sac-like  dilatations,  the  alveoli  or  acini  (Fig.  ioo,  </<?). 
The  best  example  of  a  compound  alveolar  gland  is  the  mammary 
gland,  although  the  lung  is  constructed  on  the  principle  of  a  com- 
pound alveolar  gland. 

Certain  structures  remain  to  be  considered  which  are  properly 
classified  as  glands,  but  in  which  during  development  the  ex- 
cretory duct  has  disappeared.  Such  glands  are  known  as  ductless 
glands. 

The  ovary  is  a  ductless  gland,  the  specific  secretion  of  which,  the 
ovum,  is  under  normal  conditions  taken  up  by  the  oviduct  and  car- 
ried to  the  uterus.     This  is  known  as  a  dehiscent  gland. 

Other  ductless  glands,  such  as  the  thyroid  and  adrenal,  are  known 
as  glands  of  internal  secretion,  their  specific  secretions  passing  direct- 
ly into  the  blood  or  lymph  systems. 


174  THE   ORGANS. 

A  few  glands,  e.g.,  the  liver  and  pancreas,  have  both  an  internal 
secretion  and  an  external  secretion. 

General  Structure  of  Mucous  Membranes. 

The  alimentary  tract,  the  respiratory  tubules,  parts  of  the  genito- 
urinary system,  and  some  of  the  organs  of  special  sense  are  lined  by 
mucous  membranes.  While  differing  as  to  details  in  different  organs, 
the  general  structure  of  all  mucous  membranes  is  similar.  The  essen- 
tial parts  are  (i)  surface  epithelium,  (2)  basement  membrane,  and 
(3)  stroma  or  tunica  propria.  The  epithelium  may  be  simple  colum- 
nar, as  in  the  gastro-intestinal  canal;  ciliated,  as  in  the  bronchi; 
stratified  squamous,  as  in  the  oesophagus,  etc.  The  epithelium  rests 
upon  a  basement  membrane  or  membrana  propria  which,  like  the  same 
membrane  in  glands,  is  described  by  some  as  a  product  of  the  epithe- 
lium, by  others  as  a  modification  of  the  underlying  connective  tissue. 
Beneath  the  basement  membrane  is  a  connective-tissue  stroma,  or 
tunica  propria.  This  usually  consists  of  loosely  arranged  fibrous 
tissue  with  some  elastic  fibres.  It  may  contain  smooth  muscle  cells 
and  lymphoid  tissue. 

In  addition  to  the  three  layers  above  described  there  is  frequently 
a  fourth  layer  between  the  stroma  and  the  submucosa.  This  con- 
sists of  one  or  more  layers  of  smooth  muscle,  and  is  known  as  the 
muscularis  mucosce. 

A  mucous  membrane  usually  rests  upon  a  layer  of  connective 
tissue  rich  in  blood-vessels,  lymphatics,  and  nerves — the  submucosa. 


CHAPTER    VI. 

THE    DIGESTIVE    SYSTEM. 

The  digestive  system  consists  of  the  alimentary  tract  and  certain 
associated  structures  such  as  glands,  teeth,  etc. 

The  alimentary  tract  is  a  tube  extending  from  lips  to  anus. 
Different  parts  of  the  tube  present  modifications  both  as  to  calibre 
and  as  to  structure  of  wall. 

The  embryological  subdivision  of  the  canal  into  headgut,  foregut, 
midgut,  and  endgut  admits  of  further  subdivision  upon  an  anatomical 
basis  as  follows  : 

I.   Headgut :    (a)  Mouth,  including  the  tongue  and  teeth. 
(/;)   Pharynx. 
II.   Foregut:     (a)   GEsophagus. 
(/;)   Stomach. 

III.  Midgut :  Small  intestine. 

IV.  Endgut :      (a)   Large  intestine. 

(b)   Rectum. 

The  entire  canal  is  lined  by  mucous  membrane,  the  modifications 
of  which  constitute  the  most  essential  difference  in  structure  of  its 
several  subdivisions. 

Beneath  the  mucosa  is  usually  more  or  less  connective  tissue, 
which  in  a  large  portion  of  the  canal  forms  a  definite  submucosa. 

Muscular  tissue  is  present  beneath  the  submucosa  throughout  the 
greater  part  of  the  canal.  In  most  regions  it  forms  a  definite,  con- 
tinuous, muscular  tunic. 

The  upper  and  lower  ends  of  the  tube — mouth,  pharynx,  oesoph- 
agus, and  rectum — are  quite  firmly  attached  by  fibrous  tissue  to  the 
surrounding  structures.  The  remainder  of  the  tube  is  less  firmly 
attached,  lying  coiled  in  the  abdominal  cavity,  its  abdominal  surface 
being  covered  by  a  serous  membrane,  a  reflection  of  the  parietal 
peritoneum. 


i75 


176  THE   ORGANS. 

I.  THE    HEADGUT. 

The   Mouth. 

The  Mucous  Membrane  of  the  Mouth. — This  consists  of 
stratified  squamous  epithelium  lying  upon  a  connective-tissue  stroma 
or  tunica  propria.  The  latter  is  thrown  up  into  papilla,  which  do 
not,  however,  appear  upon  the  free  surface  of  the  epithelium.  The 
submucosa  is  a  firm  connective-tissue  layer  with  few  elastic  fibres. 
The  thickness  of  the  epithelium,  the  character  of  the  stroma,  and  the 
height  of  the  papillae  vary  in  different  parts  of  the  mouth.  There  is 
no  muscular  is  mucosas. 

At  the  junction  of  skin  and  mucous  membrane  (red  margin  of  the 
lips)  the  epithelial  layer  is  much  thickened,  the  stroma  is  thinned, 
and  the  papillae  are  very  high.  At  this  point  the  stratum  corneum 
of  the  skin  passes  over  into  the  softer  nucleated  epithelium  of  the 
mouth,  while  the  stratum  lucidum  and  stratum  granulosum  of  the 
skin  terminate  (see  skin,  page  314). 

The  mucous  membrane  of  the  gums  has  prominent,  long,  slender 
papillae,  the  summits  of  which  are  covered  by  a  very  thin  layer  of 
epithelium.  This  nearness  of  the  vascular  stroma  to  the  surface 
accounts  for  the  ease  with  which  the  gums  bleed.  That  portion  of 
the  gums  which  extends  over  the  teeth  is  devoid  of  papillae.  The 
submucosa  of  the  gums  is  firmly  attached  to  the  underlying  peri- 
osteum. 

The  mucous  membrane  lining  the  cheeks  has  low,  small  papillae, 
and  the  submucosa  is  closely  adherent  to  the  muscular  fibres  of  the 
buccinator. 

Covering  the  hard  palate,  the  mucous  membrane  is  thin  and  the 
short  papillae  are  obliquely  placed,  their  apices  being  directed  ante- 
riorly.    The  submucosa  is  firmly  attached  to  the  periosteum. 

Over  the  soft  palate  the  papillae  of  the  mucous  membrane  are  low 
or  even  absent.  They  are  somewhat  higher  on  the  uvula,  the  poste- 
rior surface  of  which  shows  a  transitional  condition  of  its  epithe- 
lium, areas  of  stratified  squamous  alternating  with  areas  of  stratified 
columnar  ciliated  epithelium.  Throughout  the  mucous  membrane  of 
the  soft  palate,  uvula,  and  fauces,  the  stroma  and  submucosa  contain 
diffuse  lymphatic  tissue.  In  some  places  the  lymphoid  cells  are  so 
closely  placed  as  to  form  distinct  nodules. 


THE  DIGESTIVE  SYSTEM.  17  7 

Glands  of  the  Oral  Mucosa.1 — Distributed  throughout  the 
oral  mucosa  are  small  branched  tubular  glands.  Only  in  those  parts 
of  the  mucous  membrane  which  are  closely  attached  to  underlying 
bone,  as  on  the  gums  and  hard  palate,  are  mucous  glands  few  or 
entirely  absent.  While  the  deeper  portions  of  the  glands  are  in  the 
submucosa,  some  of  the  tubules  usually  lie  in  the  stroma  of  the  mu- 
cous membrane. 

The  ducts  open  upon  the  surface  and  are  lined  with  a  continuation 
of  the  surface  stratified  squamous  epithelium  as  far  as  the  first  bifur- 
cation. Here  the  epithelium  becomes  stratified  columnar,  and  this, 
as  the  smaller  branches  are  approached,  passes  over  into  the  simple 
columnar  type.  Not  infrequently  ducts  of  small  secondary  glands 
empty  into  the  main  duct  during  its  passage  through  the  mucosa. 

According  to  the  character  of  their  secretions  the  oral  glands  are 
divided  into  : 

(a)  Mucous  glands,  which  secrete  a  mucin  -  containing  fluid 
(mucus) ; 

(/?)   Serous   glands,   which   secrete   a   serous   (albuminous)    fluid; 

(c)  Mixed  glands,  the  secretion  of  which  is  partly  mucous  and 
partly  serous. 

Morphologically,  also,  a  similar  distinction  can  be  made  in  regard 
to  the  glandular  epithelium  which  lines  the  terminal  tubules,  the 
tubules  of  mucous  glands  being  lined  with  "  mucous  "  cells,  those  of 
serous  glands  with  "  serous  cells,"  while  of  the  mixed  glands  the  cells 
of  some  tubules  are  mucous,  of  others  serous.  In  certain  tubules 
both  mucous  and  serous  cells  occur.  The  appearance  which  these 
cells  present  depends  largely  upon  their  secretory  condition  at  the 
time  of  death. 

Serous  cells  when  resting  have  a  slightly  granular  protoplasm, 
which  in  the  fresh  condition  is  highly  refractive,  giving  the  cells  a 
transparent  appearance.  With  the  beginning  of  secretion  the  gran- 
ules increase  in  number  and  the  cells  become  darker.  Stained  with 
hcematoxylin-eosin,  serous  tubules  have  a  pink  or  bluish-pink  color. 
The  nuclei  are  spherical  or  oval,  and  are  situated  between  the  centre 
and  base  of  the  cell  (Fig.  135,  p.  220.) 

Mucous  cells  are  in  the  quiescent  state  rather  small  cuboidal  or 
pyramidal  cells,  with  cloudy  cytoplasm  and  nuclei  situated  at  the 
base  of  the  cell.      When  active  the  mucous  cells  are  much  larger,  with 

1  For  description  of  the  larger  salivary  glands  see  page  217. 
12 


178  THE   ORGANS. 

clear  cytoplasm  and  with  nuclei  flattened  against  the  basement  mem- 
brane. Mucous  tubules  are  larger  and  more  irregular  in  shape  than 
serous  tubules,  and  when  stained  with  haematoxylin-eosin  either 
remain  almost  wholly  unstained  or  take  a  pale  blue  hematoxylin 
stain  (Fig.  135,  p.  220).  Many  mucous  tubules  have  in  addition  to 
the  mucous  cells  a  peculiar,  often  crescentic-shaped  group  of  cells  on 
one  side  of  the  tubule,  between  the  mucous  cells  and  the  basement 
membrane.  These  cells  are  granular,  stain  rather  deeply  with  eosin, 
and  resemble  serous  cells.  On  account  of  the  shape  of  the  groups, 
they  are  known  as  the  crescents  of  Gianuzsi  or  demilunes  of  Heiden- 
Jiain  (Fig.  135,  p.  220).  The  cells  of  the  crescents  are  connected 
with  the  lumen  by  means  of  secretory  tubules,  which  pass  between 
the  mucous  cells  and  end  in  branches  within  the  protoplasm  of  the 
crescent  cells. 

Peculiar  irregular  branching  cells  have  been  described,  extending 
from  the  basement  membrane  in  between  the  mucous  cells.  They 
are  known  as  "basket"  cells  and  are  supposed  to  be  supportive  in 
character. 

The  cells  of  both  mucous  and  serous  tubules  rest  upon  a  mem- 
brana  propria,  outside  of  which,  separating  the  tubules,  is  a  cellular 
connective-tissue  stroma. 

Of  the  small  glands  of  the  mouth,  a  group  near  the  root  of  the 
tongue  are  of  the  mucous  variety,  some  "  lingual  "  glands  in  the 
region  of  the  circumvallate  papilla?  are  serous,  while  the  remainder 
are  of  the  mixed  type. 

Blood-vessels. — The  larger  vessels  run  mainly  in  the  submucosa. 
The  arteries  of  the  submucosa  give  off  one  group  of  branches  to  the 
tunica  propria,  where  they  break  up  into  a  dense  subepithelial  capil- 
lary network,  sending  capillary  loops  into  the  papillae.  A  second 
group  of  arterial  branches  pass  to  the  submucosa,  where  they  give 
rise  to  capillary  networks  among  the  tubules  of  the  mucous  glands. 
From  the  capillaries  veins  arise  which  accompany  the  arteries. 

Lymphatics. — The  larger  lymph  vessels  lie  in  the  submucosa. 
These  send  smaller  branches  into  the  tunica  propria,  where  they  open 
into  small  lymph  capillaries  and  spaces. 

Nerves. — Medullated  nerve  fibres  form  plexuses  in  the  submucosa 
and  deeper  parts  of  the  mucosa.  From  these  plexuses,  branches  are 
given  off  which  lose  their  medullary  sheaths  and  form  a  second 
plexus  of  non-medullated  fibres  just  beneath  the  epithelium.      From 


THE  DIGESTIVE  SYSTEM.  179 

this  subepithelial  plexus,  branches  pass  in  between  the  epithelial  cells 
to  terminate  in  end  brushes  or  in  tactile  corpuscles  (see  nerve  end- 
ings, page  348).  The  nerves  belong  to  the  cerebro-spinal  system, 
and  are  dendrites  of  sensory  ganglion  cells.  Axones  of  sympathetic 
neurones  are  also  present  in  the  oral  mucosa,  destined  mainly  for  the 
muscle-tissue  of  the  blood-vessels. 

TECHNIC. 

(1)  The  superficial  cells  of  the  oral  mucous  membrane  may  be  prepared  for 
examination  as  in  technic  1,  page  46. 

(2)  For  the  study  of  the  mucous  membrane  of  different  parts  of  the  mouth,  fix 
small  pieces  in  formalin-Muller's  fluid  (technic  5,  p.  5),  cut  sections  perpendicular 
to  the  surface,  stain  with  haematoxylin-eosin  (technic  1,  p.  16),  and  mount  in  balsam. 

(3)  Small  mucous  and  serous  glands  of  the  mouth  may  be  studied  in  the  pre- 
ceding sections. 

The  Tongue. 

The  tongue  is  composed  mainly  of  striated  muscle  fibres,  sup- 
ported by  connective  tissue  and  covered  by  a  mucous  membrane. 
While  the  bundles  of  fibres  interlace  in  all  directions,  three  fairly 
distinct  planes  can  be  differentiated. 

(1)  Vertical  and  somewhat  radiating  fibres — hyoglossus,  genio- 
glos-sus,  and  vertical  fibres  of  the  lingualis. 

(2)  Transverse  fibres — transverse  fibres  of  the  lingualis. 

(3)  Longitudinal  fibres — the  styloglossus  and  longitudinal  (supe- 
rior and  inferior)  fibres  of  the  lingualis. 

The  connective  tissue  which  supports  the  muscle  fibres  and  sepa- 
rates them  into  bundles  contains  mucous  glands  and  fat.  A  strong 
band  of  connective  tissue,  the  septum  lingua?,  extends  lengthwise 
through  the  middle  of  the  tongue,  dividing  it  into  right  and  left 
halves. 

The  submucosa  of  the  tongue  is  not  well  developed,  the  stroma  of 
the  mucosa  resting  directly  upon  the  underlying  muscle. 

The  mucous  membrane  of  the  tongue  resembles  that  of  the  mouth, 
but  differs  from  the  latter  in  that  in  addition  to  the  low  papillae,  such 
as  are  found  in  the  oral  mucosa,  the  upper  surface  of  the  tongue  is 
studded  with  numerous  and  much  larger  papillae  or  villi.  These  pro- 
ject from  the  surface  and  give  to  the  tongue  its  characteristic  rough- 
ness. Three  forms  of  papillae  are  distinguished.  Filiform,  fungi- 
form, and  circumvallate. 


iSo 


THE   ORGANS. 


(i)  Filiform  Papillae  (Fig.  101). — These  are  the  most  nu- 
merous and  stud  the  entire  dorsum  of  the  organ.  Each  consists  of 
a  central  core  of  connective  tissue  containing  elastic  fibres,  which  is 
long  and  slender  and  is  covered  by  stratified  squamous  epithelium. 


b— 


: 


■  v,;  a 


Lie 


■3)att 


FIG.  ioi.— Vertical  Section  through  Two  Filiform  Ppaillse  from  Human  Tongue.     X  80.     (Szy- 
monowicz. )     a,  Horny  epithelium  ;  l>,  stroma  ;  c,  epithelium  ;  d,  secondary  papilla. 

From  the  summit  of  each  papilla  are  given  off  several  secondary 
papilhe.  The  epithelium  covering  these  papilla?  is  hornified  and 
often  extends  from  the  surface  as  a  long  thread-like  projection — 
hence  the  name,  filiform. 

(2)  Fungiform  Papilltk  (Fig.  102).- — Scattered  irregularly  over 
the  entire  dorsum  among  the  filiform  papillae,  but  fewer  in  number, 
are  larger  papillae  of  somewhat  different  structure  known  as  fungiform 
papilla:-.  Their  apices  are  rounded  instead  of  pointed  and  their  bases 
are  narrowed.  Secondary  papillae  are  given  off  not  only  from  the 
summit,  but  from  the  sides  of  the  papilla.  The  epithelial  covering 
is  comparatively  thin  and  is  not  hornified.  The  connective-tissue 
core  of  these  papillae  contains  but  few  elastic  fibres. 

(3)  The  Cikcumvallate  Papill/k  (Fig.  103). — These  are  from 
nine  to  fifteen  in  number,  and  are  grouped  on  the  posterior  surface 
of  the  dorsum  of  the  tongue.     They  resemble  the  fungiform  papillx, 


THE  DIGESTIVE  SYSTEM.  18 1 

but  are  much  larger.  Each  lies  rather  deep  in  the  mucous  membrane, 
surrounded  by  a  groove  or  trench  and  wall  (whence  the  name  circum- 
vallate).  The  wall  is  somewhat  lower  than  the  papilla,  thus  allowing 
the  latter  to  project  slightly  above  the  surface.  Secondary  papillae 
are  confined  to  the  upper  surface  of  the  papilla,  the  sides  being  free 
from  secondary  papillae.  The  surface  of  the  papilla  and  the  borders 
of  the  groove  and  wall  are  covered  by  stratified  squamous  epithelium. 
Lying  in  the  epithelium  of  the  side  wall  and  sometimes  of  the  oppo- 
site trench  wall  are  oval  bodies,  the  so-called  taste  buds,  which  serve 
as  organs  for  the  nerves  of  taste  (see  nervous  system).  Into  the 
trench  surrounding  the  circumvallate  papilla  open  the  ducts  of  serous 
glands  (Ebner's  glands). 

The  lymph  follicles  of  the  tongue  have  been  already  described 
(page  141)  under  the  head  of  the  lingual  tonsils. 

For  glands  of  the  tongue  see  page  178. 

The  larger  blood-vessels  run  in  the  connective-tissue  septa. 
These  give  off  smaller  branches,  which   break  up  into  capillary  net- 


&■-  •'.   ■•-:.:;.:.•.        ,.    .     •_  ..,.,.■  *;_■:■.■;  _: ..   ;.._._: 

Fig.  102.— Vertical  Section  through  Fungiform  Papilla  of  Human  Tongue.     X  45.     (Szymono- 
wicz.)     a,  Secondary  papilla  ;  b,  epithelium  ;  c,  muscle  fibres. 

works  surrounding  the  muscle  fibres  and  forming  a  plexus  just  be- 
neath the  epithelium.      From  the   latter  are  given  off  capillaries   to 


I  82 


THE   ORGANS. 


the  papillae.     The  capillaries  converge  to  form  veins,  which  in  gen- 
eral follow  the  course  of  the  arteries. 

Fine  lymph  spaces  occur  in  the  papillae  and  open  into  a  plexus  of 
small  lymph  capillaries  just  beneath  the  papillae.  These  communi- 
cate with  a  deeper  plexus  of  larger  lymphatics,  which  increase  in  size 


Jui 


W- 


FlG.  103. — Vertical  Section  through  a  Cireumvallate  Papilla  of  Human  Tongue.  X  37.  (Szy- 
monowicz.)  a.  Secondary  papilla  ;  b,  wall ;  c,  trench  ;  d,  epithelium  of  tongue  ;  <\  stroma  ; 
/,  submucosa  ;  g,  Ebner's  glands. 

and  number  as  they  pass  backward  and  form  an  especially  dense  lym- 
phatic network  at  the  root  of  the  tongue  in  the  region  of  the  lingual 
tonsils. 

Nerves. — Sympathetic  fibres  pass  mainly  to  the  smooth  muscle  of 
the  blood-vessels  and  to  the  glands.  Medullated  motor  nerve  fibres 
supply  the  lingual  muscles.  (For  motor  nerve  endings  see  page 
353.)  Medullated  sensory  nerves  include  those  of  the  special  sense 
of  taste  as  well  as  those  of  ordinary  sensation.  They  end  freely 
among  the  epithelial  cells  or  in  connection  with  special  end-organs — 
the  taste  buds  mainly  in  the  cireumvallate  papillae,  and  the  end- 
bulbs  of  Krause  in  the  fungiform  papillae  (see  page  349). 

TECHNIC. 

Remove  pieces  of  the  dorsum  of  the  tongue,  selecting  parts  thai  will  include 
the  different  forms  of  papillae  and  cutting  well  into  the  underlying  muscular  tissue. 


THE  DIGESTIVE  SYSTEM. 


183 


Treat  as  in  technic  2,  p.  179,  or  sections  may  be  stained  with  haematoxylin-picro- 
acid-fuchsin  (technic  3,  p.  16). 

In  sections  from  the  back  part  of  the  tongue  good  examples  of  mucous  and 
serous  glands  are  usually  found. 

In  small  sections  of  the  tongue  the  muscle  fibres  are  seen  arranged  in  bundles, 
surrounded  by  connective  tissue  and  interlacing  in  all  directions.  For  the  study  of 
the  arrangement  of  the  different  planes  of  muscle,  complete  transverse  sections 
should  be  made  at  intervals  through  the  entire  tongue.  The  muscle  and  connec- 
tive-tissue relations  are  best  brought  out  by  the  haematoxylin-picro-acid-fuchsin 
stain. 

The  Teeth. 

A  tooth  is  a  hard  bone-like  structure,  part  of  which  projects 
above  the  surface  of  the  jaw  as  the  crown,  while  the  deeper  portion, 
the  root,  is  buried  in  a  socket  of  the 
alveolar  margin  (Fig.  104). 

A  tooth  consists  of  a  soft  central 
core,  the  pulp  cavity,  surrounded  by 
dentine  (Figs.  104  and  105).  The 
latter  constitutes  the  main  bulk  of  the 
tooth.  The  exposed  portion  of  the 
dentine  is  covered  by  a  thin  layer  of 
extremely  hard  substance,  the  enamel 
(Fig.  104,  /),  while  the  alveolar  por- 
tion of  the  dentine  is  covered  with 
cementum  (Fig.  104,  J).  Of  these  the 
dentine  and  cementum  are  of  connec- 
tive-tissue origin,  the  enamel  of  epi- 
thelial. 

The  pulp  cavity  occupies  the  cen- 
tral axis  of  the  tooth  (Figs.  104  and 
105).  In  the  root  it  is  known  as  the 
root  canal.  At  the  apex  of  the  root 
it  communicates  with  the  underlying 
tissue  by  means  of  a  minute  open- 
ing, through  which  blood-vessels  and 
nerves  enter  the  pulp  cavity. 

The  dentinal  pulp  consists  of  loose 
connective    tissue    of    an     embryonal 
type,  composed  of  fusiform   and   stel- 
late cells    and    delicate   fibrils   not  joined    to    form  bundles.      This 
tissue  supports   the  blood-vessels  and  nerves  which  are  found   onlv 


FIG.  104. — Vertical  Section  of  Tooth  in 
Situ.  X  15.  (Waldeyer.)  <r.  Pulp 
cavity,  the  letter  being  at  about  the 
junction  of  crown  and  root  ;  /,  enamel 
showing  radial  and  longitudinal  mark- 
ings ;  2,  dentine  showing  dental  ca- 
nals; 3,  cementum  (containing  bone 
corpuscles)  ;  4,  dental  periosteum  :  5. 
bone  of  lower  jaw. 


1 84  THE   ORGANS. 

in  the  pulp  of  the  tooth.  The  surface  of  the  pulp  is  covered  by 
a  single  layer  of  columnar  cells,  the  odontoblasts.  These  cells  are 
closely  allied  to  osteoblasts.  Their  nuclei  lie  toward  their  inner 
ends.     Each  cell  sends  out  an  inner  process,  which  is  usually  single 

A" 


& 

!*'j» 


~A   -■* 


'  *  ml  J,   *    i 


*  ■  i*   >! 
**■*    I 

•■*-**  £- 

:  **»   V 

te  1 

*  *  *  k 

1  *■  * .      & 


\'  >»  11./  ' 


/>* 


FIG.  105.— Cross-section  through  Root  of  Human  Canine  Tooth  (X  25)  (Sabotta),  showing  re- 
lations of  pulp  cavity,  dentine,  and  cement  um.  /J,  Pulp  cavity  ;  D,  dentine  ;  C,  cement  uni  ; 
A',  Tomes'  granular  layer. 

and  passes  into  the  dentinal  pulp,  and  one  or  more  outer  fibre-like 
processes  which  enter  the  dentine,  where  they  form  the  dentinal 
fibres. 

DENTINE  (Figs.  106  and  107,  /))  resembles  bone.  It  is  peculiar 
in  that  it  contains  canaliculi,  dental  canals  (Figs.  106  and  107,  Dk), 
but  no  lacunas  or  bone  cells.  The  latter  are  represented  by  the 
odontoblasts  of  the  pulp,  which,  as  already  noted,  lie  at  the  inner  side 
of  the  dentine,  into  the  canaliculi  of  which  they  send  the  dentinal 
fibres.      Dentine   is  non-vascular.     The  dental  canals  begin  at  the 


THE  DIGESTIVE  SYSTEM. 


185 


dental  pulp,  where  they  have  a  calibre  of  2  to  3  //..  They  pass  out- 
ward, taking  a  somewhat  curved  course,  to  the  limit  of  the  dentine. 
In  their  passage  through  the  dentine  the  main  canals  give  off  side 
branches,  which  anastomose  with  similar  branches  from  other  canals. 
This  anastomosis  takes  place  not  only  between  branches  of  adjacent 
canals,  but  also  between  branches  of  canals  some  distance  apart. 
The  main  canals  terminate  either  in  blind  extremities,  or  form  loops 
by  anastomosing  with  neighboring  tubules.  A  few  tubules  run 
slightly  beyond  the  limits  of  the  dentine  into  the  enamel.  They  do 
not  pass  into  the  cementum.  The  dentine  immediately  around  a 
dental  canal  is  more  dense  and  hard  than  elsewhere  and  forms  a  sort 
of  sheath  for  the  canal — Neumann  s  dental  sheath.  Between  the 
dental  canals  is  a  calcified  ground  substance,  in  which  are  connec- 
tive-tissue fibres  running  in  the  long  axis  of  the  tooth. 

Spaces  which  probably  represent  incomplete  calcification  of  the 
dentine  occur  in  the  peripheral  portion  of  the  dentine  of  the  crown. 


KB 


Dk 


Fig.  106.— From  Longitudinal  Section  through  Root  of  Human  Molar  Tooth  (x  200)  (Sabotta), 
showing  junction  of  dentine  and  cementum.  C,  Cementum  ;  D,  dentine  ;  A",  Tomes' 
granular  layer  ;  Dk,  dental  canals  ;  KH,  lacunas  of  cementum. 


These  are  known  as   interglobular  spaces  (Fig.    107,  Jg).      They  are 
filled  with  a  substance  resembling  uncalcified  dentine. 

In  the  outer  part   of  the   dentine  of  the  root  are  similar  spaces 


iS6 


THE   ORGANS. 


which  are  smaller  and  more  closely  placed.     These  form  the  so-called 
Tomes'  granular  layer  (Fig.  106,  A'). 

The  enamel  is  the  hardest  substance  in  the  body.  It  contains 
little  more  than  a  trace  of  organic  substance  (3  to  5  per  cent).  It 
consists  of  long  six-sided  prisms — enamel  fibres  or  enamel  prisms 
(Fig.  107,  5) — which  take  a  slightly  wavy  course  through  the  entire 
thickness  of  the  enamel.  The  prisms  are  attached  to  one  another  by 
a  small  amount  of  cement  substance.     In  the  human  adult  the  prisms 


>Jg 


FIG.  107. — From  Longitudinal  Section  of  Crown  of  Human  Premolar  (X  200)  (Sabotta),  show- 
ing junction  of  enamel  and  dentine.  S,  Enamel;  D,  dentine;  Sfl,  enamel  prisms;  Dk, 
dental  canals;/^-,  interglobular  spaces.  A  few  dentinal  fibres  are  seen  passing  beyond 
the  limits  of  the  dentine  into  the  enamel.  The  oblique  dark  bands  in  the  enamel  are  the 
lines  of  Retzius. 

arc  homogeneous  ;  in  the  embryo  they  show  a  longitudinal  fibrillation. 
Rather  indistinct  parallel  lines  (the  lines  oi  Retzius)  cross  the  enamel 
prisms.  They  probably  represent  the  deposition  in  layers  of  the  lime 
salts.  The  enamel  is  covered  by  an  apparently  structureless  mem- 
brane, the  cuticula  dentis. 

The  CEMENTUM  (Fig.  1 06,  C)  covers  the  dentine  of  the  root  in  a 
manner  similar  to  that  in  which  the  enamel  covers  the  dentine  of  the 
crown  (Fig.  104,  /  and  J).  Cementum  is  bone  tissue.  It  contains 
ha  it nt.e  and  bone  cells,  but  no  distinct  lamellation  and  no  Haversian 
systems  or  blood-vessels,  excepting  in  the  large  teeth   of  the  larger 


THE  DIGESTIVE  SYSTEM.  187 

mammalia,  where  they  may  be  present.  Many  uncalcified  Sharpey's 
fibres  penetrate  the  cementum. 

The  union  between  the  root  of  the  tooth  and  the  alveolar  peri- 
osteum is  accomplished  by  a  reflection  of  the  latter  over  the  root, 
where  it  forms  the  dental  periosteum,  or  peridental  membrane  (Fig. 
104,  4).  At  the  neck  of  the  tooth  this  membrane  blends  with  the 
submucosa  of  the  gum.  The  peridental  membrane  is  formed  of 
fibrillar  connective  tissue  free  from  elastic  fibres.  These  fibres  are 
directly  continuous  with  Sharpey's  fibres  of  the  cementum. 

Blood-vessels  of  teeth  are  confined  entirely  to  the  pulp  cavity. 
One  or  two  small  arteries  reach  the  pulp  cavity  from  the  underlying 
connective  tissue,  through  the  foramen  in  the  apex  of  the  root. 
These  break  up  into  a  capillary  network  in  the  dental  pulp. 

Lymphatics  have  as  yet  not  been  demonstrated  in  the  dental  pulp. 

Medullated  nerve  fibres  accompany  the  blood-vessels  through  the 
apical  canal.  In  the  pulp  they  break  up  into  a  number  of  non- 
medullated  branches,  which  form  a  plexus  along  the  outer  edge  of 
the  pulp,  beneath  the  odontoblasts.  From  this  plexus  branches  are 
given  off  which  pass  in  between  the  odontoblasts,  some  terminating 
there,  while  others  end  between  the  odontoblasts  and  the  dentine. 

Development. — The  enamel  of  the  teeth  is  of  ectodermic  origin, 
the  remainder  of  mesodermic.  The  earliest  indication  of  tooth 
formation  occurs  about  the  seventh  week  of  intra-uterine  life.  It 
consists  in  a  dipping  clown  of  the  epithelium  covering  the  edge  of 
the  jaw  into  the  underlying  connective  tissue,  where  it  forms  the 
dental  ridge,  or  common  dental  germ.  At  intervals  along  the  outer 
side  of  this  dental  ridge,  the  cells  of  the  ridge  undergo  proliferation 
and  form  thickenings,  ten  in  number,  each  one  corresponding  to  the 
position  of  a  future  milk  tooth.  These  are  known  as  special  dental 
germs,  and  remain  for  some  time  connected  with  one  another  and 
with  the  surface  epithelium  by  means  of  the  rest  of  the  dental  ridge. 

Into  the  under  side  of  each  special  dental  germ  an  invagination 
of  the  underlying  connective  tissue  occurs.  This  forms  the  dental 
papilla  (Fig.  108),  over  which  the  tissue  of  the  special  dental  germ 
forms  a  sort  cf  a  cap,  the  latter  being  known  from  its  subsequent 
function  as  the  enamel  organ.  The  next  step  is  the  almost  complete 
separation  of  the  special  dental  germs  and  ridge  from  the  surface 
epithelium  (Fig.  108),  and  the  formation  around  each  special  dental 
Eferm  of  a  vascular  membrane,  the  dental  sac.      The  attenuated  strand 


1 88  THE   ORGANS. 

of  epithelial  cells,  which  still  maintains  a  connection  between  the 
dental  germs  and  the  epithelium  of  the  gums,  is  known  as  the 
neck  of  the  enamel  organ,  and  it  is  from  this  that  an  extension  soon 
occurs  to  the  inner  side  of  the  dental  germs  of  the  milk  teeth,  to 
form  the  dental  germs  of  the  permanent  teeth  (Fig.  108).  Into  the 
latter,  connective-tissue  papillae  extend  as  in  the  case  of  the  milk 
teeth.  There  are  thus  present  as  early  as  the  fifth  month  of  fretal 
existence  the  germs  of  all  milk  and  of  some  permanent  teeth. 

The  enamel  organ  at  this  stage  consists  of  three  layers:   (i)   The 
outer  enamel  cells,  somewhat  flattened ;   (2)  the  inner  enamel  cells, 


h- 


—  b 


\ 

■*■—■" 


** 


Fig.  108.— Developing  Tooth  from  Three-and-one-half-months'  Human  Embryo.  X  65.  (Szy- 
monowicz.)  </,  Epithelium  of  gums;  6,  neck  of  enamel  organ;  c,  dental  germ  of  permanent 
tooth  ;  ./,  bone  of  lower  jaw  ;  e,  dental  papilla;/;  inner  enamel  cells;.;',  enamel  pulp;  It, 
outer  enamel  cells. 

high  columnar  epithelium;  (3)  a  layer  of  enamel  pulp,  situated 
between  the  other  layers,  and  consisting  of  stellate  anastomosing 
tells  with  considerable  intercellular  substance  (Figs.    108  and  109). 

The  first  of  the  dental   tissue  to  become  hard   is  the   DENTINE. 
The  surface  cells  of  the  papilla  differentiate  to  form  a  layer  of  colum- 


THE  DIGESTIVE  SYSTEM. 


189 


■       •  ■   c  (  J) 


■V 


nar  cells,  odontoblasts.  Between  these  and  the  inner  enamel  cells  a 
membrane-like  structure,  the  membrane/,  prcsformativa,  is  formed. 
This  becomes  converted  into  den- 
tine by  the  deposition  of  lime  salts, 
the  process  being  similar  to  the 
formation  of  bone  by  the  osteoblasts. 
Processes  of  the  odontoblasts  remain 
in  the  developing  dentine  as  the 
dental  fibres,  lying  in  channels,  the 
dental  canals.  Additional  dentine 
continues  to  be  laid  down  in  layers, 
each  new  layer  internal  to  the  pre- 
ceding. In  this  way  the  dental 
papilla  is  reduced  in  size  to  form 
the  pulp  cavity.  Small  spots  re- 
main, in  which  there  is  little  or  no 
calcification.  These  are  the  so- 
called  interglobular  spaces. 

The  emamel  is  formed  by  the 
enamel  organ.  A  membrane,  the 
cuticular  membrane,  is  first  laid 
down  between  the  inner  enamel 
cells  and  the  dentine.  Each  of  the 
inner  enamel  cells  now  sends  out  a 
process,  Tomes'1  process,  from  its 
inner  end.  The  processes  are  separated  by  a  considerable  amount  of 
cement,  and  are  the  beginnings  of  the  enamel  prisms.  Calcification 
now  takes  place  both  in  the  prisms  and  in  the  cement  substance,  the 
latter  at  the  same  time  becoming  reduced  in  amount.  Further 
growth  in  thickness  of  enamel  occurs  by  lengthening  of  the  enamel 
prisms.  During  the  formation  of  the  enamel,  the  enamel  pulp  and 
the  external  enamel  cells  disappear. 

The   cementum  is   developed  by  ossification  of  that  part  of  the 
dental  sac  which  covers  the  root. 


.,... 


m 

y  : 


-—%-m 


'® 


-  ^mmm 


Fig.  109.— From  Cross-section  through  a  De- 
veloping Tooth.  X  720.  (Bohm  and  von 
Davidoff  )  Note  close  relationship  be- 
tween odontoblasts  and  tissue  of  dental 
pulp.  <?,  Dental  pulp  ;  b,  odontoblasts  ;  c, 
dentine  ;  d,  inner  enamel  cells  ;  e,  enamel 
pulp. 


TECHNIC. 

(1)  Teeth  are  extremely  difficult  organs  from  which  to  obtain  satisfactory  ma- 
terial for  study.  Sections  of  hard  (undecalcified)  and  of  decalcified  teeth  may  be 
prepared  in  the  same  manner  as  sections  of  bone — technics  1  and  2,  p.  156.  The 
decalcified  tooth  should  include  if  possible  the  alveolar  margin  of  the  jaw,  so  that 


i go  THE   ORGANS. 

in  longitudinal  sections  the  mode  of  implantation  and  the  relation  of  the  tooth  to 
the  surrounding  structures  can  be  seen. 

(2)  For  the  study  of  developing  teeth,  em bryo  pigs,  sheep,  cats,  dogs,  etc.,  are 
suitable.  For  the  early  stages  foetal  pigs  should  be  five  to  six  inches  long;  for  the 
intermediate,  ten  to  twelve  inches.  The  later  stages  are  best  obtained  from  a  small 
new-born  animal,  e.g. ,  kitten  or  small  pup.  The  jaw — preferably  the  lower — or 
pieces  of  the  jaw  are  fixed  in  formalin-Muller's  fluid  (technic  5,  p.  5),  hardened 
in  alcohol,  and  decalcified  (page  S).  Subsequent  treatment  is  the  same  as  for  de- 
veloping bone  (technic  1.  p.  164). 

The   Pharynx. 

The  wall  of  the  pharynx  consists  of  three  coats — mucous,  mus- 
cular, and  fibrous. 

1.  The  mucous  membrane  has  a  surface  epithelium  and  an  un- 
derlying stroma. 

The  epithelium  is  stratified  squamous  except  in  the  region  of 
the  posterior  nares,  where  it  is  stratified  columnar  ciliated,  contin- 
uous with  the  similar  epithelium  of  the  nasal  mucosa. 

The  stroma,  or  tunica  propria,  consists  of  mixed  fibrous  and  elas- 
tic tissue  infiltrated  with  lymphoid  cells.  In  certain  regions  these 
cells  form  distinct  lymph  nodules  (see  pharyngeal  tonsils,  page  142). 
Beneath  the  stratified  squamous  epithelium  the  stroma  is  thrown  up 
into  numerous  low  papilla.  These  are  absent  in  regions  covered  by 
ciliated  cells.  Bounding  the  stroma  externally  is  a  strongly  de- 
veloped layer  of  longitudinal  elastic  fibres,  the  clastic  limiting  layer, 
which  separates  the  stroma  from  the  muscularis  and  sends  stout 
bands  in  between  the  muscle  bundles  of  the  latter. 

2.  The  muscular  coat  lies  beneath  the  elastic  layer  and  is  formed 
of  very  irregularly  arranged  muscle  fibres  belonging  to  the  constrictor 
muscles  of  the  pharynx. 

3.  The  fibrous  coat  consists  of  a  dense  network  of  mixed  fibrous 
and  elastic  tissue.  It  has  no  distinct  external  limit,  and  binds  the 
pharynx  to  the  surrounding  structures. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  is  simi- 
lar to  that  in  the  oral  mucosa. 

Small,  branched,  tubular,  mucous  glands  are  present  in  the  stroma, 
and  extend  down  into  the  intermuscular  connective  tissue.  They 
are  most  numerous  near  the  opening  of  the  Eustachian  tube. 

TECHNIC. 

For  the  study  of  the  structure  of  the  walls  of  the  pharynx,  material  should 
be  prepared  as  in  technic  2.  p.  170. 


THE  DIGESTIVE  SYSTEM. 


191 


THE  FOREGUT. 

The  (Esophagus. 

The  walls  of  the  oesophagus  are  continuous  with  those  of  the 
pharynx  and  closely  resemble  the  latter  in  structure.  They  consist 
of  four  layers,  which  from  within  outward  are  mucous,  submucous, 
muscular,  and  fibrous  (Fig.  no). 


f.  ;<# 


-  ft 


Fig.  no.— Transverse  Section  through  Wall  of  Dog's  Oesophagus.  X  18.  (Bohm  and  von  Da- 
vidoff.)  (/,  Epithelium;  6,  stroma;  c,  muscularis  mucosas;  d,  submucosa  ;  e,  circular 
muscle  layer  ;  f,  longitudinal  muscle  layer  ;  g,  fibrous  layer. 

i.  The  mucous  membrane  resembles  that  of  the  pharynx  except 
that  beneath  the  stroma  is  a  well-developed  muscularis  mucosa  com- 
posed of  smooth  muscle  cells  arranged  longitudinally. 

2.  The  submucosa  is  composed  of  loosely  arranged  fibrous  and 
elastic  tissue.  It  contains  mucous  glands,  the  larger  blood-vessels, 
lymphatics,  and  nerves. 

3.  The  muscular  coat.  In  the  upper  portion  of  the  oesophagus 
this  coat  is  composed  of  striated  muscle  fibres;  in  the  middle  portion 
of  mixed  striated  and  smooth  muscle.      In  the  lower  portion  there  are 


192  THE   ORGANS. 

two  distinct  layers  of  smooth  muscle,  an  inner  circular  and  an  outer 
longitudinal.      The  latter  is  not  continuous. 

4.  The  fibrous  coat  consists  of  bundles  of  white  fibrous  tissue 
with  many  elastic  fibres.  It  serves  to  connect  the  oesophagus  with 
the  surrounding  structures. 

Two  kinds  of  glands  occur  in  the  oesophagus. 

(i)  Mucous  Glands. — These  are  of  the  same  structure  as  those 
of  the  tongue,  but  much  smaller.  They  lie  in  the  submucosa  and  are 
distributed  throughout  the  entire  oesophagus,  though  most  numerous 
in  its  upper  third.  The  ducts  pass  obliquely  downward  on  their  way 
to  the  surface.  Just  before  entering  the  muscularis  mucosae  the  duct 
widens  out  to  form  a  sort  of  ampulla.  Beyond  this  it  again  becomes 
narrow  and  enters  the  epithelium  in  the  depression  between  two 
adjacent  papillae.  A  small  lymph  nodule  is  usually  attached  to  the 
duct  as  it  passes  through  the  tunica  propria. 

(2)  Simple  Branched  Tubular  Glands. — These  resemble  the 
glands  of  the  cardiac  end  of  the  stomach,  but  branch  much  more 
profusely.  Some  contain  both  chief  and  acid  cells,  others  only  chief 
cells  (see  stomach,  page  195).  They  lie  in  the  tunica  propria,  and 
are  for  the  most  part  confined  to  a  narrow  zone  at  the  lower  end  of 
the  oesophagus  and  to  the  level  of  the  fifth  tracheal  ring.  Scattered 
groups  also  occur  in  other  regions. 

TECHNIC. 

Remove  a  portion  of  the  wall  of  the  oesophagus,  wash  carefully  in  normal 
salt  solution,  and  pin  out,  mucous-membrane  side  up,  on  a  piece  of  cork.  Fix  in 
formalin-Muller's  fluid  and  harden  in  alcohol  (technic  5,  p.  5).  Transverse  or 
."ongitudinal  sections  should  be  cut  through  the  entire  thickness  of  the  wall.  If 
the  details  of  the  muscular  coat  are  to  be  studied,  sections  from  at  least  three  dif- 
ferent levels  should  be  taken  :  one  near  the  upper  end,  one  at  about  the  middle,  and 
the  other  in  the  lower  third.  Stain  with  hsmatoxylin-eosin  or  ha;matoxylin-picro- 
acid-fuchsin  (technic  1  or  3,  p.  16)   and  mount  in  balsam. 

General  Structure  ok  the  Walls  of  the  Gastro-Intestinal 

Canal. 

The  walls  of  the  stomach  and  intestines  are  made  up  of  four  coats 
(T~ig.  mi).  These  from  the  lumen  outward  are  mucous,  submucous, 
muscular,  and  serous. 

1.  The  mucous  membrane  (Fie.  1  1  1)  consists  of  surface  epithe- 


THE  DIGESTIVE  SYSTEM. 


*93 


Hum,  gland  stroma,  and  muscularis  mucosae.  The  surface  epithe- 
lium is  simple  columnar  and  rests  upon  a  distinct  basement  membrane. 
The  arrangement  of  the  glands  and  the  nature  of  the  gland  cells  differ 
in  different  parts  of  the  tract.  The  stroma  is  a  richly  cellulai  con- 
nective tissue,  which   in  some  places  is  so  infiltrated  with  lymphoid 


PlG.  hi.  —  Diagram  of  Structure  of  Wall  of  Gastro-intestinal  Canal.  A,  Mucous  membrane; 
a,  glands  ;  b,  epithelium  ;  c,  goblet  cells  ;  d,  stroma  ;  e,  inner  circular,  /,  outer  longitudi- 
nal layers  of  g;  muscularis  mucosae.  5,  Submucosa.  C,  Muscular  coat  ;  //,  its  inner  cir- 
cular layer:  /,  its  outer  longitudinal  layer  ;  /,  intermuscular  connective-tissue  septum. 
D,  serous  coat  ;  k,  its  connective-tissue  layer  ;  /,  its  endothelial  layer. 

cells  as  to  constitute  diffuse  lymphatic  tissue.  In  other  places  it 
contains  circumscribed  masses  of  lymphatic  tissue,  lymph  nodules. 
The  amount  of  stroma  depends  upon  the  closeness  with  which  the 
glands  are  packed.  The  muscularis  mucosce  consists  of  smooth 
muscle  cells,  which  have  a  generally  longitudinal  arrangement. 
Where,  however,  the  muscularis  mucosas  is  thick  there  are  frequently 
J3 


194  THE   ORGAXS. 

two  distinct  layers — an  inner  circular  and  an  outer  longitudinal. 
Folds  of  considerable  extent  occur  in  the  mucous  membrane.  Those 
of  the  stomach  are  known  as  rtigce,  and  are  not  constant,  depend- 
ing upon  the  degree  of  distention  of  the  organ.  Those  of  the 
small  intestine  are  much  more  definite,  and  are  known  as  valvules 
connive  ntcs. 

2.  The  submucosa  (Fig.  1 1 1)  is  a  loose  connective-tissue  struc- 
ture.     It  contains  the  larger  blood-vessels,  lymphatics,  and  nerves. 

3.  The  muscular  coat  (Fig.  1 1 1)  consists  of  two  layers  of  smooth 
muscle,  which  in  the  intestine  are  sharply  differentiated  into  an  inner 
circular  and  an  outer  longitudinal.  In  the  stomach  the  direction  of 
the  layers  of  the  muscularis  is  less  definite.  A  narrow  layer  of  con- 
nective tissue  separates  the  two  layers  of  muscle.  From  this,  septa 
extend  into  the  muscle  tissue,  separating  it  into  bundles. 

4.  The  serous  coat  (Fig.  1 1 1)  is  the  visceral  layer  of  the  peri- 
toneum. It  consists  of  a  thin  layer  of  connective  tissue  covered  by 
a  single  layer  of  mesothelium.  Along  the  attachment  of  the  mesen- 
tery the  serous  coat  is  wanting. 

The  subdivisions  of  the  gastro-intestinal  canal  differ  from  one 
another  mainly  in  regard  to  the  structure  of  their  mucous  mem- 
branes, and  especially  in  regard  to  the  structure  of  the  glands  of  the 
mucous  membrane  and  submucosa. 


The  Stomach. 

I.  The  mucous  membrane  of  the  stomach  is  often  folded  into 
ridges  or  rugce,  the  height  of  which  depends,  as  already  noted,  upon 
the  degree  of  distention  of  the  organ.  The  rugae  are  most  promi- 
nent in  the  collapsed  organ,  almost  absent  when  the  organ  is  fully 
distended.  In  addition  to  the  rugae  the  entire  mucous  membrane  is 
studded  with  minute  depressions  barely  visible  to  the  naked  eye, 
the  so-called  gastric  pit s  or  crypts  (Fig.  1  12,  Mg).  These  mark  the 
openings  of  the  gastric  glands.  In  the  fundus  they  are  compara- 
tively shallow,  extending  through  about  one-fifth  the  thickness  of  the 
mucosa ;  in  the  pylorus  the  crypts  are  much  deeper,  extending  through 
half  or  more  of  the  thickness  of  the  mucous  membrane  (compare 
Figs.  1 12  and  1  16). 

'flic  Epithelium. — At  the  junction  of  oesophagus  (Fig.  1  13)  and 


THE  DIGESTIVE  SYSTEM. 


195 


stomach  the  stratified  squamous  epithelium  of  the  former  ends  rather 
abruptly,  being  replaced  by  the  simple  columnar  epithelium,  which 
covers  the  entire  surface  of  the  gastric  mucosa  and  extends  down  into 
the  crypts  (Fig.  112).  The  cells  are  of 
the  high,  clear,  mucous  type  (Fig.  114, 
M  and  M' ).  The  end  of  the  cell  tow- 
ard the  lumen  is  clear,  usually  consists 
mostly  of  mucus,  and  consequently 
stains  lightly.  The  basal  end  of  the 
cell  contains  the  spheroidal,  oval,  or 
sometimes  flattened  nucleus,  is  granular, 
and  takes  a  darker  stain.  The  cells  rest 
upon  a  distinct  basement  membrane. 

The  Gastric  Glands. — Extending 
from  the  bottoms  of  the  crypts,  their 
epithelium  continuous  with  that  of  the 
crypts  themselves,  are  the  gastric  glands. 
These  are  of  two  kinds,  peptic  or  fundus 
glands,  distributed  throughout  the  greater 
part  of  the  gastric  mucosa,  and  pyloric 
glands,  confined  to  the  immediate  region 
of  the  pylorus. 

The  peptic  glands  (Fig.  1 1 2)  are 
simple,  sometimes  branched,  tubular 
glands,  of  which  from  three  to  seven 
open  into  each  gastric  crypt.  They  ex- 
tend through  the  entire  thickness  of  the 
stroma,  to  the  muscularis  mucosae. 

Each  gland  consists  of  (1)  a  mouth 
opening  into  the  crypt ;  (2)  a  constricted 
portion,  the  neck;  (3)  the  body  or  main 
portion  of  the  tubule ;  and  (4)  a  slightly 
dilated  and  bent  blind  extremity,  the  fundus  (Fig.  112).  The 
mouth  marks  the  transition  from  the  higher  epithelium  of  the  crypt 
to  the  low  cuboidal  of  the  neck  (Fig.  114,  //).  In  the  body  and 
fundus  of  the  gland  two  types  of  cells  are  found :  (a)  chief  cells  (cen- 
tral, peptic,  or  adelomorphous),  and  (b)  parietal  cells  (acid,  oxyntic, 
or  delomorphous). 

The  chief  cells  (Fig.   114,  a)  are  the  more  numerous.      They  are 


Fig.  112.— Vertical  Section  through 
the  Mucous  Membrane  of  the  Fun- 
dus of  the  Stomach.  X  85.  (K61- 
liker.)  Mg,  Gastric  crypts  ;  //, 
neck  ;  k,  body  ;  g;  fundus  of  peptic 
glands;  //,  chief  cells;  £,  parietal 
cells  ;  m,  muscularis  mucosae. 


196 


THE   ORGANS. 


of  the  low  columnar  type,  often  pyramidal  with  apices  directed  toward 
the  lumen.  Their  protoplasm  is  granular  and  clear,  taking  a  light 
stain.  Their  bases  rest  either  on  the  basement  membrane  or  against 
the  parietal  cells. 

The  parietal  cells  (Fig.  114,  b)  are  oval  or  polygonal  in  shape, 
and  lie  against  the  basement  membrane.  The  nucleus  is  spherical, 
somewhat  larger  than  that  of  the  chief  cell,  and  is  usually  situated 
at  the  centre  of  the  cell.  The  protoplasm  is  finely  granular  and 
stains  intensely  with  the  aniline  dyes.  In  stained  specimens  the  two 
kinds  of  cells  are  thus  in  marked  contrast.      Although  lying  against 


1  -Section  through  Junction  of  (Esophagus  and  Stomach  of  Man.  X  121.  (Schilffer.) 
Oe,  Oesophagus  :  .1/,  stomach  ;  cd,  cardiac  glands  ;  wd,  dilated  ducts  of  cardiac  glands  ;  S, 
stroma;  /:',  stratified  squamous  epithelium  of  oesophagus;  mm,  muscularis  mucosae ;  cd, 
irregularly  cut  tubules  of  cardiac  glands  ;  </</,  cardiac  glands  in  lower  end  of  the  oesoph- 
agus ;  it,  limit  of  stratified  oesophageal  epil  helium. 

the  basement  membrane  and  frequently  pushing  il  out  so  as  to  form 
little  protuberances  beyond  the  even  line  of  the  gland  tubule,  the 
parietal  cells  always  maintain  a  connection  with  the  lumen.  This  is 
accomplished  by  means  of  little  clefts   between  the  chief  cells  {inter- 


THE  DIGESTIVE  SYSTEM. 


197 


jq^X 


/ , 


cclhdar  secretory  tubules),  which  extend  down  to  the  parietal  cells. 
By  means  of  the  method  of  Golgi  may  be  demonstrated  not  only  the 
intercellular  secretory  tubules,  but  also  the  fact  that  upon  reaching 
the  cells  these  are  continuous  with  a 
network  of  minute  spaces  within 
the  cell — the  intracellular  secretory 
tubules  (Fig.  115).  Parietal  cells  are 
not  distributed  uniformly  through- 
out the  gland,  but  are  most  numer- 
ous in  the  body,  where  they  fre- 
quently almost  obscure  the  chief 
cells.  In  the  fundus  parietal  cells 
are  usually  less  numerous.  For  this 
reason  and  because  of  the  wider 
lumen  of  the  fundus,  transverse  and 
longitudinal  sections  of  this  part  of 
the  tubule  are  most  satisfactory  for 
the  study  of  the  relations  of  the 
two  kinds  of  cells  (Figs.  1 1 2  and 
114). 

Lying  near  the  basement  mem- 
brane between  the  bases  of  the  col- 
umnar epithelial  cells  are  small 
spherical  or  irregular  cells  with 
dark  nuclei.  These  are  young  epithelial  cells  which  from  their  func- 
tion are  known  as  "replacing  cells  "  (see  page  56). 

The  pyloric  glands  (Figs.  116  and  117)  are  simple  branched 
tubular  glands,  several  of  which  open  into  each  of  the  deep  pyloric 
crypts.  The  glands,  though  short,  are  quite  tortuous,  so  that  in  sec- 
tions the  tubules  are  seen  cut  mainly  transversely  or  obliquely.  In 
most  of  the  pyloric  glands  but  one  type  of  cell  is  found.  These 
resemble  the  chief  cells  of  the  fundus,  but  present  a  more  uniform 
appearance,  probably  due  to  the  absence  of  parietal  cells.  As  in  the 
fundus,  "replacing  cells  "  lie  between  the  bases  of  the  columnar  epi- 
thelial cells.  Parietal  cells  are  not  always  entirely  absent,  but  occur 
here  and  there  in  the  pyloric  tubules,  especially  near  the  fundus. 

The  transition  from  fundus  to  pylorus  is  not  abrupt,  but  is  marked 
by  a  "transitional  border  zone,"  in  which  fundus  and  pyloric  glands 
are  intermingled. 


Fig.  114. — Cross-sections  at  Various  Levels 
of  Peptic  Glands  of  Stomach.  X  400. 
(Kolliker.)  M,  Section  through  gastric 
pit  near  surface  ;  M' ',  section  through  gas- 
tric pit  near  bottom  ;  //,  mouth  of  gland  ; 
k,  neck  ;  g;  bod;'  near  fundus  ;  a,  chief 
cells;  b,  parietal  cells. 


198 


THE   ORGANS, 


In  the  transition  zone  between  oesophagus  and  stomach  are  found 
glands  which  resemble  the  peptic  glands,  but  contain  no  parietal 
cells. 

The  stroma  (Figs.  112  and  116)  or  tunica  propria,  in  which 
the   glands  are  embedded,  consists   of   mixed  fibrillar  and   reticular 

connective  tissue  infiltrated  with  lymphoid 
cells.  In  the  fundus  the  glands  are  so 
closely  packed  that  the  stroma  is  reduced 
to  thin  strands,  which  pass  up  between  the 
glands  and  separate  the  fundi  from  the 
muscularis  mucosae.  In  the  pylorus  the 
glands  are  more  widely  separated  and  the 
stroma  is  correspondingly  greater  in  amount. 
In  both  fundus  and  pylorus  thicker  strands 
of  stroma  surround  a  number  of  gland  tub- 
ules, thus  separating  them  into  more  or  less 
well-defined  groups.  In  addition  to  the  dif- 
fuse lymphatic  tissue  of  the  stroma,  closely 
packed  aggregations  of  lymphoid  cells  are 
found  in  the  shape  of  distinct  nodules, 
known  as  "  solitary  follicles"  These  occur 
throughout  the  entire  gastric  mucosa,  but 
are  most  numerous  in  the  pylorus.  The 
nodules  are  usually  egg-shaped,  their  apices 
lying  just  beneath  the  epithelium,  their 
bases  resting  upon  the  muscularis  mucosas. 
Less  commonly  they  lie  partly  in  the  sub- 
mucosa.  Over  the  nodules  the  epithelium 
is  more  or  less  infiltrated  with  migratory 
leucocytes.  Most  of  the  nodules  contain 
germinal  centres,  around  which  the  lym- 
phoid cells  are  more  closely  packed  than  elsewhere  (see  page  132). 

The  muscularis  mucosa:  (Figs.  112  and  116,  m)  may  consist  of 
a  single  layer  of  smooth  muscle  with  cells  arranged  longitudinally  or 
obliquely,  or  there  may  be  two  distinct  layers,  an  inner  circular  and 
an  outer  longitudinal.  From  the  muscularis  mucosae  single  cells 
and  roups  of  cells  extend  into  the  stroma  between  the  gland  tubules. 
2.  The  submucosa  consists  of  connective  tissue,  loosely  arranged, 
and  contains  lar^e  blood-vessels. 


FIG.  115.— Longitudinal  Section 
of  Portion  of  Body  of  Gland 
from  Fundus  of  Cat's  Stom- 
ach. Golgi  stain,  fixed  in 
ammonium  sulphide  and 
haimatoxylin-eosin  counter- 
stains,  showing  lumen  and 
intracellular  secretory  tu- 
bules of  parietal  cells.  (Zim- 
mermann.) 


THE  DIGESTIVE  SYSTEM. 


199 


3.  The  muscular  coat  is  usually  described  as  consisting  of  three 

layers,  an  inner  oblique,  a  middle  circular,  and  an  outer  longitudinal. 

This  division  of  the  muscular  coat   into  layers  having  definite 


*  ^SS* 


rm'V    1   f 


i\0i  [f^Mf  it  ikv 


Fig.  116.  Fig.  117. 

Fig.  116.— Vertical    Section    through   Mucous   Membrane   of   Pyloric    End   of   Stomach.     X 

S5.     (Kolliker.)     Mgs  Gastric  crypt ;    6,  blood-vessel  in  stroma  ;  d,  longitudinal   section 

of  body  of  gland  ;  m,  muscularis  mucosas. 
FlG.  117.  — Pyloric  Gland  from  Vertical  Section  through  Wall  of  Dog's  Stomach.     (Ebstein.)    m, 

Gastric  pit  in  which  are  seen  some  transversely  cut  cells  ;  n,  neck  of  gland  ;  f,  fundus 

cut  transversely. 

directions  can  be  made  out  only  in  the  pylorus,  the  muscle  bundles 
of  the  fundus  running  in  various  directions. 

4.   The  serous  coat  consists  of  a  layer  of  loosely  arranged  connec- 
tive tissue  covered  by  a  single  layer  of  mesothelium. 


TECHNIC. 

(1)  Remove  a  human  stomach  (not  more  than  two  or  three  hours  after  death) 
or  that  of  a  recently  killed  dog.  Open  along  the  lesser  curvature,  and  carefully  re- 
move the  excess  of  mucus  by  washing  with  normal  saline.     Cut  pieces  through 


200  THE   ORGANS. 

the  entire  thickness  of  the  wall,  one  from  the  fundus  and  one  from  the  pylorus; 
pin  out.  mucous  membrane  side  up.  on  pieces  of  cork,  fix  in  formalin-Miiller's  fluid 
(technic  5,  p.  5)  or  in  Zenker's  fluid  (technic  9.  p.  6),  and  harden  in  alcohol.  Sec- 
tions are  cut  as  thin  as  possible,  care  being  taken  that  the  plane  is  such  that  the 
glands  are  cut  longitudinally,  stained  with  haematoxylin-eosin  (technic  i.p.  16), 
and  mounted  in  balsam. 

(2)  Instead  of  removing  pieces  of  stomach  and  pinning  them  out  on  cork,  as 
suggested  in  the  preceding  technic.  the  entire  stomach  may  be  filled  with  the  fixa- 
tive, the  ends  being  tied,  and  then  placed  in  a  large  quantity  of  the  fixing  fluid. 
After  fixation,  pieces  are  removed  and  hardened  in  graded  alcohols.  If  this 
method  is  used,  great  care  must  be  taken  not  to  overdistend  the  organ,  only  very 
moderate  distention  being  desirable.  Further  treatment  is  the  same  as  in  the  pre- 
ceding technic  (1). 

(3)  For  comparison  of  resting  with  active  gastric  cells,  preparations  should  be 
made  from  the  stomach  of  an  animal  that  has  been  for  from  twenty-four  to  forty- 
eight  hours  without  food,  and  from  a  stomach  during  active  digestion.  Fix  in 
Zenker's  fluid  as  in  technic  (1),  above.  Examine  unstained  sections  and  sections 
stained  with  haematoxylin-eosin. 

(4)  Sections  through  the  junction  of  oesophagus  and  stomach  and  through  the 
junction  of  stomach  and  duodenum  furnish  instructive  pictures.  They  should  be 
prepared  as  in  technic  (1). 

(5)  For  the  study  of  the  distribution  of  the  blood-vessels  sections  of  an  injected 
stomach  should  be  made.  This  is  best  accomplished  by  selecting  a  small  animal, 
such  as  a  rat  or  guinea-pig,  and  injecting  in  toto  through  the  ascending  aorta,  or 
by  injecting  only  the  hind  part  of  the  animal  through  the  abdominal  aorta.  Tech- 
nic, p.  20. 

III.  THE   MIDGUT. 

The  Small  Intestine. 

On  passing  from  stomach  to  small  intestine  the  rugae  of  the 
former  disappear,  but  are  replaced  by  much  more  definite  foldings  of 
the  mucosa,  the  valvules  conniventes  (Fig.  119).  These  folds  involve 
the  entire  thickness  of  the  mucous  membrane  and  part  of  the  sub- 
mucosa.  They  are  in  general  parallel  to  one  another,  and  pass  in  a 
circular  or  oblique  manner,  partly  around  the  lumen  of  the  gut.  The 
entire  surface  of  the  intestine,  including  the  valvulae,  is  studded  with 
minute  projections  just  visible  to  the  naked  eye,  and  known  as  villi 
(Figs.  1  19  and  120).  These  involve  only  the  epithelium  and  stroma, 
although  they  also  contain  some  muscular  elements  derived  from  the 
muscularis  mucosas.  The  villi  differ  in  shape  in  the  different  parts 
of  the  small  intestine,  being  leaf-shaped  in  the  duodenum,  rounded 
in  the  jejunum,  club-shaped  in  the  ileum.  The  valvula?  conniventes 
and  the  villi  are  characteristic  of  the  small  intestine.  It  is  impor- 
tant to  note  that  while  the  crypts  of  the  stomach  are  depressions  in 


THE  DIGESTIVE  SYSTEM. 


201 


the  mucous  membrane,  the  intestinal  villi  are  definite  projections 
above  its  general  surface  (Fig.    1 18). 

The  wall  of  the  intestine  consists  of  the  same  four  coats  described 
as  constituting  the  wall  of  the  stomach,  mucosa,  subnutcosa,  museu- 
laris,  and  fibrosa. 

i.  The  mucosa,  as  in  the  stomach,  is  composed  of  a  lining  epithe- 
lium, stroma,  glands,  and  muscularis  mucosa?.      Of  these  the  epithe- 


FlG.  118.-  Section  through  Junction  of  Pylorus  and  Duodenum.  (Klein.)  v.  Villi  of  duode- 
num ;  d,  stomach,  showing  gastric  crypts;  b,  apex  of  a  solitary  lymph  nodule;  c,  crypt  of 
Lieberkiihn  ;  s,  secreting  tubules  of  Brunner's  glands  ;  ^",  pyloric  glands  ;  /,  tubules  of 
Brunner's  glands  in  submucosa  of  stomach  ;  m,  muscularis  mucosae. 

lium,  the  stroma,  and  cells  from  the  muscularis  mucosae  are  concerned 
in  the  formation  of  the  villi. 

The  villus  consists  of  a  central  core — a  fold  of  the  stroma — of 
mixed  fibrous  and  reticular  tissue  infiltrated  with  lymphoid  cells,  and 
of  a  covering  epithelium. 

The  epithelium  is  of  the  simple  columnar  type.  The  cells  are 
high  and  have  thickened  striated  free  borders  (Figs.  12 1  and  122). 
These  contiguous  thickened  free  borders  unite  to  form  a  distinct 
membrane,  the  cuticular  membrane  (Fig.  122,  c).  Scattered  among 
the  columnar  cells  are  numerous  mucous  or  goblet  cells  (Figs.  121 
and  122,  b).  The  goblet  cells  are  derived  from  the  columnar  cells, 
and  vary  in  appearance  according  to  the  amount  of  secretion  which 


202 


THE   ORGANS. 


they  contain.  A  cell  at  the  beginning  of  secretion  contains  only 
a  small  amount  of  mucus  near  its  free  border.  As  secretion  in- 
creases  the   mucus  gradually  replaces  the   cytoplasm   until   the  lat- 


Mm 


x  x 


(runp 


,,  JS  f|  xS  fr ; 


a. — 


FIG.  119.— Vertical  Longitudinal  Section  of  Human  Jejunum  (X  16)  (Stohr),  including  two  val- 
vulae  conniventes.  a,  Villi,  in  many  of  which  the  stroma  has  shrunken  away  from  the 
epithelium  leaving  a  clear  space,  X  X.  Lying  free  in  the  lumen  of  the  gut  are  seen  sec- 
tions of  villi  cut  in  various  directions.  />,  Epithelium  ;  c,  stroma  ;  d,  crypts  of  Lieberkiihn  ; 
X,  solitary  lymph  nodule  with  germinal  centre  ;  e,  tissue  of  submucosa  forming  centre  of 
one  of  the  valvulas  conniventes  ;  f,  submucosa  ;  g,  inner  circular  layer  of  muscle  ;  //,  outer 
longitudinal  layer  of  muscle  ;  z\  Auerbach's  plexus  ;•/,  serous  coat. 

ter  is  represented  only  by  a  crescentic  mass  containing  a  flat- 
tened nucleus  and  pressed  against  the  basement  membrane.  The 
cell  now  discharges  its  mucus  upon  the  free  surface.  The  goblet 
cells  possess  no  thickened  border,  appearing,  when  seen  from  the 
surface,  as  openings  surrounded  on  all  sides  by  the  cuticulae  of  the 
adjacent  columnar  cells.  Small  spherical  cells  with  deeply  staining 
nuclei  are  found  in  varying  numbers  among  the  epithelial  cells. 
These  are  so-called  wandering  cells,  migratory  leucocytes,  from  the 
underlying  stroma  (Figs.  121,  //,  and  122,  /).  Other  cells  with  dark- 
staining  nuclei,  "  replacing  cells,''  are  found  between  the  bases  of  the 
columnar  cells  (pages  56  and  [97). 

In   addition   to   the  connective-tissue  and   lymphoid  cells,  which 


THE  DIGESTIVE  SYSTEM. 


203 


constitute  the  main  bulk  of  the  villus  core  (Figs.  121  and  122),  iso- 
lated smooth  muscle  cells  derived  from  the  muscularis  mucosae  occur, 
running  in  the  long  axis  of  the  villus.  A  single  lymph  or  chyle 
vessel  (Fig.  121,  f;  122,  cli)  with  distinct  endothelial  walls  traverses 
the  centre  of  each  villus,  ending  at  its  tip  in  a  slightly  dilated  blind 
extremity.  As  it  is  usually  seen  collapsed,  it  appears  as  two  closely 
approximated  rows  of  flat  cells  with  bulging  nuclei.  The  capillaries 
of  the  villus  lie  for  the  most  part  away  from  the  chyle  vessel,  just 
beneath  the  basement  membrane  (Fig.  121,  e ;   122,  g). 

From  the  depths  of  the  depressions  between  the  villi,  simple 
tubular  glands — glands  or  crypts  of  Lieberkuhn  (Figs.  120  and 
123) — extend  down  through  the  stroma  as  far  as  the  muscularis  mu- 
cosae. These  crypts  are  lined  with  an  epithelium  similar  to  and  con- 
tinuous with  that  covering  the  villi.      The  cells  are,  however,  lower, 


Fig.  120.— Vertical  Section  through  Mucous  Membrane  of  Human  Jejunum.  X  80.  (Stohr.) 
j  and  b,  Artifacts  due  to  shrinkage;  c,  intestinal  crypts  (Lieberkuhn);  d,  oblique  and 
transverse  sections  of  crypts  ;  e,  stroma  ;f,  epithelium  ;  g;  tangentially  cut  villi  ;  //,  mus- 
cularis mucosas  ;  i,  submucosa. 


and  there  are  fewer  goblet  cells.  In  addition  to  these  cells  there  are 
also  found  in  the  depths  of  the  crypts  of  Lieberkuhn  peculiar  coarsely 
granular  cells,  the  cells  of  Paneth  (Fig.  123,  k).      They  are  found  in 


204 


THE   ORG  Ays. 


man  and  in  rodents,  but  do  not  occur  in  the  carnivora.      They  prob- 
ably produce  a  specific  secretion,  the  nature  of  which  is  unknown. 

The  stroma,  besides  forming  the  centres  of  the  villi,  fills  in  the 
spaces  between  the  crypts  of  Lieberkiihn  and  between  the  latter  and 


Fig.  121. 


-i 


gm 


■y?-':-'iiL-"  <''-'-s-^ 


KlK  m  ©IP  %3$c 


■  —  --  '-.^ys^m^:  ■  -t# 3 


WP      z'A*)  J^r"* -—-'  -' .'^K 


i$ 


^^ 


Fig.  122. 


FIG.  i2i.—  Longitudinal  Section  of  Vilhis  from  Small  Intestine  of  Dog.  (Piersol.)  ./,  Colum- 
nar epithelium  ;  b<  goblet  cells  ;  A,  leucocytes  ;  c,  basement  membrane  :  d,  core  of  villus  ; 
e,  blood  vessels  ;  f,  lacteal. 

FIG.  122 — Cross-section  of  a  Villus  of  Human  Small  Intestine.  X  530.  CKolliker.)  The  stroma 
of  the  villus  has  shrunken  away  from  the  epithelium.  />,  Goblet  cell  ;  c,  cuticula  showing 
striations;  e,  columnar  epithelial  cell  ;  jr»i,  basement  membrane  with  nuclei  ;  /,  leucocyte 
in  epithelium  ;  /',  leucocyte  just  beneath  epithelium  ;  ;;/,  large  leucocyte  in  stroma  ;  c/i, 
central  chyle  vessel  ;  g,  blood-vessel. 


the  muscularis  mucosae.  In  places  the  lymphoid  cells  are  closely 
packed  to  form  distinct  nodules  or  "  solitary  follicles,"  such  as  are 
found  in  the  stomach  (see  page  198). 

Peyer's  Patches  (agminated  follicles)  (Fig.  124). — These  are 
groups  of  lymph  nodules  found  mainly  in  the  ileum,  especially  near 
its  junction  with  the  jejunum.  They  always  occur  on  the  side  of 
the  gut  opposite  to  the  attachment  of  the  mesentery.  Each  patch 
consists  of  from  ten  to  seventy  nodules,  so  arranged  that  the  entire 
patch  has  a  generally  oval  shape,  its  long  diameter  lying  lengthwise 
of  the  intestine.     The  nodules  of  which  a  patch  is  composed  lie  side 


THE  DIGESTIVE  SYSTEM. 


205 


by  side.  Their  apices  are  directed  toward  the  lumen  and  project 
almost  through  the  mucosa,  being  uncovered  by  villi,  a  single  layer 
of  columnar  epithelium  alone  separating  their  surfaces  from  the  lumen 
of  the  gut.  The  bases  of  the  nodules  are  not  confined  to  the  stroma, 
but  usually  spread  out  in  the  submucosa.  The  relation  of  the  patch 
to  the  stroma  and  submucosa  can  be  best  appreciated  by  following 
the  course  of  the  muscularis  mucosae.  This  is  seen  to  stop  abruptly 
at  the  circumference  of  the  patch,  appearing  throughout  the  patch  as 
isolated  groups  of  smooth  muscle  cells.  The  nodules  rarely  remain 
distinct,  but  are  confluent  with  the  exception  of  their  apices  and 
bases.  It  should  be  noted  that  both  solitary  nodules  and  Peyer's 
patches  are  structures  of  the  mucosa, 
and  that  their  presence  in  the  submu- 
cosa is  secondary. 

The  MUSCULARIS  MUCOS/E  (Figs.  120 
and  125)  consists  of  an  inner  circular 
and  an  outer  longitudinal  layer  of 
smooth  muscle. 

2.  The  submucosa  (Figs.  119,  120, 
125)  consists,  as  in  the  stomach,  of 
loosely  arranged  connective  tissue  and 
contains  the  larger  blood-vessels.  It 
is  free  from  glands  except  in  the  duo- 
denum, where  it  contains  the  glands  of 
Brunner  (Fig.  125).  These  are  branched 
tubular  glands  lined  with  a  granular 
columnar  epithelium  similar  to  that  of 
the  pyloric  glands.  The  ducts  are  also 
lined  with  simple  columnar  epithelium.  "^.^  ^  >' 

They    pass    through    the  mUSCularis  mu-    Fig.    123.  -  Longitudinal     Section    of 
n  ...  r        Fundus  of  Cr}-pt  of  Lieberkuhn.     X 

cosae  and  empty  either  into  a  crypt  of 
Lieberkuhn  or  on  the  surface  between 
the  villi.  Brunner's  glands  frequently 
occur  in  the  pylorus,  and  it  is  not  un- 
common for  the  pyloric  glands  to  ex- 
tend downward  somewhat  into  the  duodenum.  Meissners  plexus 
of  nerve  fibres,  mingled  with  groups  of  sympathetic  ganglion  cells, 
lies  in  the  submucosa  (see  page  214). 

3.  The  muscular  coat  (Figs.  119  and  125)  consists  of  two  well- 


530.  (Kolliker.)  b,  Goblet  cell  show- 
ing mitosis  ;  e,  epithelial  cell  ;  A,  cell 
of  Paneth  ;  /,  leucocyte  in  epithe- 
lium ;  m,  mitosis  in  epithelial  cell. 
Surrounding  the  crypt  is  seen  the 
stroma  of  the  mucous  membrane. 


:o6 


THE  ORGANS. 


defined  layers  of  smooth  muscle,  an  inner  circular  and  an  outer  longi- 
tudinal. Connective-tissue  septa  divide  the  muscle  cells  into  groups 
or  bundles,  while  between  the  two  layers  of  muscle  is  a  connective- 


FlG.  124.— Transverse  Section  of  Cat's  Small  Intestine  through  a  Peyer's  Patch.  (Stohr.)  </, 
Villi  ;  b,  crypts  ;  c,  longitudinal  muscle  layer  ;  d,  circular  muscle  layer  ;  ey  lymph  nodules  ; 
/',  muscularis  mucosa?  ;  g,  submucosa. 

tissue  septum  which  varies  greatly  in  thickness  at  different  places 
and  contains  a  plexus  of  nerve  fibres  and  sympathetic  ganglion  cells 
known  as  the  plexus  of  Auerbach  (see  page  213). 

4.  The  serous  coat  consists  as  in  the  stomach  of  loose  connective 
tissue  covered  by  a  single  layer  of  mesothelium. 


IV.   THE    ENDGUT. 

The  Large  Intestine. 

The  wall  of  the  large  intestine  consists  of  the  same  four  coats 
which  have  been  described  as  constituting  the  walls  of  the  stomach 
and  small  intestine,  mucous,  submucous,  muscular,  and  serous. 

1.  The  mucous  membrane  has  a  comparatively  smooth  surface, 
there  being  neither  crypts  as  in  the  stomach  nor  villi  as  in  the  small 
intestine  (Fig.  126).      The  glands  are  of  the  simple  tubular  variety, 


THE  DIGESTIVE  SYSTEM. 


207 


are  considerably  longer  than  those  of  the  small  intestine,  are  almost 
straight,  and  extend  through  the  entire  thickness  of  the  stroma. 
Owing  to  the  closeness  with  which  the  gland  tubules  are  packed,  the 
amount  of  stroma  is  usually  small.  The  surface  cells  (Fig.  127,  e) 
are  very  high  and  narrow,  with  small,  deeply  placed  nuclei,  and  are 
not  usually  intermingled  with  goblet  cells.  Passing  from  the  sur- 
face down  into  the  glands,  the  cells  become  somewhat  lower  and 
goblet  cells  become  numerous  (Fig.  127,  B  and  C).  Both  super- 
ficial and  deep  cells  rest  upon  a  basement  membrane  similar  to  that 
in  the  small  intestine.  The  stroma  also,  though  less  in  amount,  is 
similar  in  structure  to  the  stroma 
of  the  small  intestine. 

The  MUSCULARIS  MUCOSA 
(Fig.  126)  consists  of  an  inner 
circular  and  an  outer  longitud- 
inal layer  of  smooth  muscle. 

2.  The  submucosa  (Fig. 
126)  consists  of  loosely  arranged 
connective  tissue.  It  contains 
large  blood-vessels  and  the  nerve 
plexus  of  Meissner  (see  page 
114).  Solitary  lymph  follicles 
occur  throughout  the  mucous 
membrane  of  the  large  intes- 
tine. While  properly  consid- 
ered as  structures  of  the  stroma 
from  which  they  originate,  the 
follicles  lie  mainly  in  the  sub- 
mucosa. (For  details  of  struct- 
ure see  page  132.) 

3.  Of  the  muscularis  (Fig. 
126)  the  inner  circular  layer 
only  is  complete,  the  muscle 
tissue  of  the  external  longitud- 
inal coat  being  arranged  mainly  as  three  strong,  flat,  longitudinal 
bands,  the  lineae  coli.  Between  these  bands  the  longitudinal  mus- 
cular coat  is  either  very  thin  or  entirely  absent.  In  the  connective 
tissue,  lying  to  the  outer  side  of  the  circular  muscle  coat,  is  the 
nerve  plexus  of  Auerbach.     (For  details  see  page  113.) 


;^>J^v^/ 


"R.\-. 

FIG.  125.— From  Vertical  Longitudinal  Section 
of  Cat's  Duodenum  to  show  Brunner's 
Glands.  (Larrabee.)  cz,  Villus;  />,  epithe- 
lium ;  c,  stroma ;  if,  crypts  ;  e,  muscularis 
mucosas  ;  /,  Brunner's  glands  ;  g;  submu- 
cosa ;  //,  circular  muscle  layer. 


208 


THE   ORGANS. 


4.  The  serous  coat  consists,  as  in  the  stomach  and  small  intestine, 
of  loose  connective  tissue  covered  by  a  single  layer  of  mesothelium. 

The  Vermiform  Appendix. 

The  vermiform  appendix  is  a  diverticulum  from  the  large   intes- 
tine.     Its  walls  are  continuous  with  those  of  the  latter,  and  closely 


Fig.  126.  Fig.  127. 

PlG.  126.— From  Vertical  Longitudinal  Section  of  Cat's  Large  Intestine.  (LarrabeeO  a 
Epithelium  ;  /<,  stroma  ;  c,  fundus  of  gland  ;  </,  muscularis  mucosae  ;  e,  submucosa  ;/,  cir- 
cular muscle  layer  ;  g,   longitudinal  muscle  layer  ;  //,  serous  coat  ;  i,  Auerbach's  plexus. 

Pig.  127.  Longitudinal  and  Transverse  Sections  of  Tubular  Glands  of  Large  Intestine,  x  149. 
'Kolliker  )  A,  Longitudinal  section;  S,  cross-section  near  mouth;  C,  cross-section 
near  middle  ;  D  and  /:',  cross-sections  near  fundus  ;  i\  surface  epithelium  ;  /,  leucocytes; 
b,  goblet  cells  :  m.  columnar  epithelium. 


resemble  them  in  general  structure.      There  are  the  same  four  coats, 
mucous,  submucous,  muscular,  and  serous. 


THE  DIGESTIVE  SYSTEM. 


109 


i.  The  mucous  membrane  (Fig.  128)  consists  of  epithelium, 
glands,  stroma,  and  muscularis  mucosae.  The  epithelium  resembles 
that  of  the  large  intestine.  The  glands  vary  in  number,  but  are 
usually  much  less  closely  packed  than  in  the  large  intestine.  They 
are  most  numerous  in  the  appendices  of  infants  and  children.  The 
o-land  tubules  (Fig.  128,  C)  are  usually  rudimentary,  but  in  most  cases 


l  m % 


MAI 


%lll§Sffii§a/ 


LN J6 


Sm  - 


Fig.  128.— Transverse  Section  of  Human  Vermiform  Appendix.  (Larrabee.)  E,  Epithelium  "• 
C,  gland  tubules  ;  Sm,  submucosa  ;  MM,  muscularis  mucosas  ;  L  N,  lymph  node  ;  C  M, 
circular  muscle  layer  ;  L  M,  longitudinal  muscle  layer. 


have  the  same  structure  as  the  intestinal  glands,  and  are  evidently 
functional  as  they  contain  mucous  cells  in  all  stages  of  secretion.  In 
consequence  of  the  wider  separation  of  the  tubules  the  stroma  is  more 
abundant  than  in  the  large  intestine,  but  has  the  same  structure. 
The  muscularis  mucosa  (Fig.  128,  MM)  is  usually  fairly  distinct  as 
a  thin  circularly  disposed  band  of  smooth  muscle  cells  just  beneath 
the  stroma.  In  some  cases  the  mucosa  as  such  is  practically  absent, 
being  replaced  by  fibrous  tissue.  This  condition  is  especially  com- 
mon after  middle  age,  and  may  or  may  not  be  associated  with  oblit- 
eration of  the  lumen. 
14 


2  10  THE   ORGANS. 

2.  The  submucosa  (Fig.  128,  S;u)  is  similar  to  that  of  the 
intestine. 

3.  The  muscular  coat  varies  greatly,  both  as  to  thickness  and 
as  to  the  amount  of  admixture  of  fibrous  tissue.  The  inner  circular 
layer  (Fig.  128,  CM)  is  usually  thick  and  well  developed.  The  outer 
longitudinal  layer  (Fig.  128,  LM)  differs' from  that  of  the  large  in- 
testine in  having  no  arrangement  into  lineae  forming  a  continuous 
layer.  Less  commonly  a  more  or  less  marked  tendency  to  anar- 
rangement  of  the  cells  of  the  longitudinal  coat  into  bundles,  between 
which  the  outer  coat  is  thin  or  wanting,  is  observed. 

4.  The  serosa  has  the  usual  structure  of  peritoneum. 

The  lymph  nodules  (Fig.  128,  L  N)  constitute  the  most  con- 
spicuous feature  of  the  appendix.  They  lie  mainly  in  the  submucosa. 
In  children  and  in  young  adults  the  nodules  are  oval  or  spherical ;  in 
later  life  somewhat  flattened.  The  nodules  may  be  entirely  distinct, 
or  may  be  arranged  as  in  a  Peyer's  patch  with  distinct  apices  and 
bases,  but  \vith  their  central  portions  confluent.  The  muscularis 
mucosae  either  passes  through  the  superficial  portions  of  the 
nodules,  or,  where  they  are  separated  from  the  lumen,  passes  over 
them. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  is  similar 
to  that  in  the  large  intestine. 

The  Rectum. 

1.  The  mucous  membrane  of  the  rectum  has  a  structure  similar 
to  that  of  the  large  intestine.  The  glands  are  longer  and  the  mucosa 
consequently  is  somewhat  thicker.  In  the  lower  part  of  the  rectum 
definite  longitudinal  foldings  of  the  mucosa  occur,  the  so-called 
columnce  rectales.  A  change  in  the  character  of  the  mucous  mem- 
brane begins  at  the  upper  end  of  the  columnar  rectales.  Here  the 
simple  columnar  epithelium  of  the  gut  passes  over  into  a  stratified 
squamous  epithelium,  beneath  which  is  a  papillated  stroma.  The 
glands  continue  for  a  short  distance  beyond  the  change  in  the  epi- 
thelium, but  soon  completely  disappear.  At  the  anus  there  is  a 
transition  from  mucous  membrane  to  skin  similar  to  that  described 
as  occurring  at  the  margin  of  the  lips  (page  176). 

2.  The  submucosa  is  similar  in  structure  to  that  of  the  large 
intestine. 


THE  DIGESTIVE  SYSTEM. 


21  I 


The  muscularis  of  the  rectum  differs  from  that  of  the  large  in- 
testine in  that  the  longitudinal  layer  is  continuous  and  thick. 

The  serous  coat  is  absent  in  the  lower  part  of  the  rectum,  being 
replaced  by  a  fibrous  connective-tissue  layer,  which  connects  the  rec- 
tum with  the  surrounding  structures. 

Blood-Vessels  of  the  Stomach  and  Intestines. 

The  arteries  reach  the  gastro-intestinal  canal  through  the  mesen- 
tery and  pass  through  the  muscular  coats  to  the  submucosa,  where 
they  form  an  extensive  plexus  of  large  vessels  (Heller's  plexus)  (Fig. 
129,  c).     Within  the  muscular  coats  the  main  arteries  give  off  small 


FlG.  129. — Scheme  of  Blood-vessels  and  Lymphatics  of  Stomach.  X  70.  (Szymonowicz,  after 
Mall.)  a,  Mucous  membrane  ;  b,  muscularis  mucosae  ;  c,  submucosa  ;  if,  inner  circular 
muscle  layer;  e,  outer  longitudinal  muscle  layer;  A,  blood-vessels;  B,  structure  of 
coats  ;  C,  lymphatics. 


branches  to  the  muscle  tissue.  From  the  plexus  of  the  submucosa 
two  main  sets  of  vessels  arise,  one  passing  outward  to  supply  the 
muscular  coats,  the  other  inward  to  supply  the  mucous  membrane 
(Fig.  129).  Of  the  former  the  larger  vessels  pass  directly  to  the 
intermuscular  septum,  where  they  form  a  plexus  from  which  branches 


2  12 


THE  ORGANS. 


are  given  off  ro  the  two  muscular  tunics.  A  few  small  branches 
from  the  larger  recurrent  vessels  also  supply  the  inner  muscular 
layer.  Of  the  branches  of  the  submucosa  plexus  which  pass  to  the 
mucous  membrane,  the  shorter  supply  the  muscularis  mucosae,  while 


Fig  130.— Scheme  of  Hlood-vessels  and  Lymphatics  of  Human  Small  Intestine.  (From  Rohm 
and  von  Davidoff,  after  Mall.)  a,  Central  lacteal  of  villus  ;  l\  lacteal  ;  c,  stroma  ;  d,  mus- 
cularis mucosae  ;  e,  submucosa  ;  /,  plexus  of  lymph  vessels  ;  £-,  circular  muscle  layer  ;  //, 
plexus  of  lymph  vessels  ;  t\  longitudinal  muscle  layer  ;  /,  serous  coat  ;  k,  vein  ;  /,  artery  ; 
m,  base  of  villus  ;  ;/,  crypt  ;  0,  artery  of  villus  ;  p,  vein  of  villus  ;  q,  epithelium. 


the  longer  branches  pierce  the  latter  to  form  a  capillary  plexus 
among  the  glands  of  the  stroma.  From  the  capillaries  small  veins 
take  origin,  which  pierce  the  muscularis  mucosae  and  form  a  close- 
meshed  venous  plexus  in  the  submucosa  (Fig.  129).  These  in  turn 
give  rise  to  larger  veins,  which  accompany  the  arteries  into  the  mes- 
entery. 

In  the  small  intestine  the  distribution  of  the  blood-vessels  is 
modified  by  the  presence  of  the  villi  (Fig.  130).  Each  villus  re- 
ceives one  small  artery,  or  in  the  case  of  the  larger  villi  two  or  three 
small  arteries.      The  artery  passes  through  the  long  axis  of  the  villus 


THE  DIGESTIVE  SYSTEM.  213 

close  under  the  epithelium  to  its  summit,  giving  off  a  network  of  fine 
capillaries,  which  for  the  most  part  lie  just  beneath  the  epithelium. 
From  these,  one  or  two  small  veins  arise  which  lie  on  the  opposite 
side  of  the  villus  from  the  artery. 

Lymphatics  of  the  Stomach  and  Intestine. 

Small  lymph  or  chyle  capillaries  begin  as  blind  canals  in  the 
stroma  of  the  mucous  membrane  among  the  tubular  glands  (Fig. 
129).  In  the  small  intestine  a  lymph  (chyle)  capillary  occupies  the 
centre  of  the  long  axis  of  each  villus,  ending  in  a  blind  extremity 
beneath  the  epithelium  of  its  summit  (Fig.  130).  These  vessels 
unite  to  form  a  narrow-meshed  plexus  of  lymph  capillaries  in  the 
deeper  part  of  the  stroma  lying  parallel  to  the  muscularis  mucosae. 
Vessels  from  this  plexus  pass  through  the  muscularis  mucosae  and 
form  a  wider  meshed  plexus  of  larger  lymph  vessels  in  the  submu- 
cosa.  A  third  lymphatic  plexus  lies  in  the  connective  tissue  which 
separates  the  two  layers  of  muscle.  From  the  plexus  in  the  submu- 
cosa,  branches  pass  through  the  inner  muscular  layer,  receive  vessels 
from  the  intermuscular  plex- 
us, and  then  pierce  the  <;!^- 
outer  muscular  layer  to  pass 
into  the  mesentery  in  com-  || 
pany  with  the  arteries  and  Gsm 
veins.                                             '>M£fi 


.0 


Nerves  of  the  Stomach  and        §mm§M 
Intestine.  '|| 

The  nerves  which  sup- 
ply the  stomach  and  intes- 
tines are    mainly  non-med- 

n    .     j  ,i      .•         j-i  FIG.  131.— Section  through  Glands  of  Fundus  of  Hu- 

Ullated      Sympathetic      fibres        man    Stomach    in    Condition    of    Hunger.       X    500. 

which     reach     the     intestinal        (Bohm  and  von   Davidoff.")     a,  Stroma;   />,  parietal 

cell ;  c,  lumen  ;  d,  chief  cell. 

walls  through  the  mesen- 
tery. In  the  connective  tissue  between  the  two  layers  of  muscle 
these  fibres  are  associated  with  groups  of  sympathetic  ganglion 
cells  to  form  the  plexus  myentericus  or  plexus  of  Auerbach.  The 
dendrites  of  the  ganglion  cells  interlace,  forming  a  large  part  of 
the  plexus.     The   axones   are  grouped  together  in  small  bundles  of 


214 


THE   ORGANS. 


non-medullated  fibres,  which  pass  into  the  muscular  coats,  where 
they  form  intricate  plexuses,  from  which  are  given  off  terminals  to 
the  smooth  muscle  cells.  From  Auerbach's  plexus  fibres  pass  to 
the  submucosa,  where  they  form  a  similar  but  finer-meshed,  more 
delicate  plexus,  also  associated  with  groups  of  sympathetic  gan- 
glion cells,  the  plexus  of  Meissner.  Both  fibres  and  cells  are  smaller 
than  those  of  Auerbach's  plexus.  From  Meissner's  plexus  delicate 
fibrils  pass  to  their  terminations  in  submucosa,  muscularis  mucosae, 
and  mucous  membrane. 

Secretion  and  the  Absorption  of  Fat. 

The  secretory  activities  of  epithelial  cells  have  already  been 
mentioned  (page  37).  The  epithelium  of  the  gastro-intestinal  tract 
must  be  considered  as  having  two  main  functions:  (1)  The  secretion 
of  substances  necessary  to  digestion ;  and  (2)  the  absorption  of  the 
products  of  digestion. 

(1)  Secretion. — The  production  of  mucus  takes  place  in  the 
mucous    or    goblet  cell,  which,  as  already  mentioned,  represents  a 


Fig.  132.— Section  through  Glands  of  Fundus  of  Human  Stomach  during  Digestion.     X  500. 
11  and  von  Davidoff.)    it,  Lumen  ;  /),  stroma  ;  c,  chief  cell  ;  rf,  parietal  cell. 


differentiation  of  the  ordinary  columnar  epithelial  cell.  The  chief 
cells,  "  peptic  cells,"  of  the  stomach  glands  arc  large  and  clear  dur- 
ing fasting,  become  granular  and  cloudy  with  the  onset  of  digestion, 


THE  DIGESTIVE  SYSTEM.  215 

and  smaller  with  loss  of  granules  during  the  digestive  process.  As 
activity  of  the  chief  cells  (Fig.  132)  is  coincident  with  an  increase  in 
the  pepsin  found  in  the  gastric  mucosa,  it  is  probable  that  these  cells 


iipil 


-^  ■  ■    -■■■■■  ■■■■  j'~zrr-"  —  ■*^P^?-«S~  ** — 


•!'■  ©  ®"         3  V©  "•■"1 


'<£>; 


©lit      ^ 


©    -<5*\      A—- 


k  ©     ft 

°      A  ©         © 


I 


■lv.   a85©      •>   -'^ 

.  •    ■  W  /yf     •  ti> 

FIG.  133. — Fat  Absorption.  Longitudinal  section  of  villus  of  cat's  small  intestine,  three  hours 
after  feeding-.  X  350.  Osmic  acid,  a,  Fat  droplets  in  epithelial  cells  ;  />,  fat  droplets  in 
leucocytes  in  stroma  ;  c,  fat  droplets  in  leucocytes  within  lacteal  ;  d,  fat  droplets  free  in 
lacteal  ;  e,  capillary  containing  blood  cells  \f,  central  lacteal  of  villus. 

produce  pepsin,  and  that  the  granules  represent  some  stage  in  the 
elaboration  of  the  ferment.  As  their  name  of  "acid  cells"  would 
indicate,  the  parietal  cells  were  considered  the  source  of  the 
hydrochloric  acid  of  the  stomach.  While  doubt  still  exists  as  to 
the  function  of  these  cells,  recent  investigations  make  it  probable 
that  it  is  not  the  secretion  of  hydrochloric  acid.  The  cells  of  Brun- 
ner's   glands   undergo    changes    during    digestion,   which    are   quite 


216  THE  ORGANS. 

similar  to  those  described  as  occurring  in  the  chief  cells  of  the 
stomach  glands,  and  are  probably  also  concerned  in  the  production 
of  pepsin.  The  only  function  of  the  intestinal  crypts  which  has 
yet  been  determined  is  the  secretion  of  mucus.  The  possibility  that 
certain  cells  of  the  crypts  of  the  small  intestine  produce  a  specific 
secretion  has  been  mentioned  (page  204). 

(2)  Absorption  of  Fat. — While  various  other  products  of  diges- 
tion are  absorbed  by  the  intestine,  the  absorption  of  fat  is  the  one 
most  easily  observed.  After  feeding  fat,  fatty  acids,  or  soaps,  fat . 
globules  are  found  to  have  penetrated  the  intestinal  mucosa,  and  may 
be  seen  in  (a)  the  epithelial  cells,  (/>)  the  leucocytes,  and  (c)  the  lac- 
teals  of  the  villi  (Fig.  133).  Fat  globules  are  never  seen  in  the 
thickened  free  borders  of  the  cells.  Hence  it  seems  probable  that 
the  fat  before  passing  through  this  part  of  the  cell  becomes  split  up 
into  glycerin  and  fatty  acids  which  are  united  again  to  form  fat 
within  the  protoplasm  of  the  cell.  Leucocytes  containing  fat  glob- 
ules are  seen  throughout  the  stroma.  Within  the  lacteals  are  found 
fat-containing  leucocytes  and  free  fat  droplets  of  various  size.  It 
would  thus  seem  probable  that  the  process  of  fat  absorption  consisted 
in  :  (1)  The  passage  of  glycerin  and  fatty  acids  through  the  cell 
borders;  (2)  their  reunion  in  the  cell  to  form  fat;  (3)  the  trans- 
ference of  these  fat  globules  to  leucocytes ;  which  (4)  carry  them  to 
the  lacteals.  In  the  lacteals  the  fat  is  probably  set  free  by  disinte- 
gration of  the  leucocytes. 

TECHNIC. 

(1)  The  technic  for  the  small  and  large  intestines  and  rectum  is  the  same  as  for 
the  stomach.  Accurate  fixation  of  the  villi  is  difficult,  there  being  usually  some 
shrinkage  of  the  connective  tissue  of  the  core  away  from  the  epithelium. 

A  longitudinal  section  should  be  made  through  the  junction  of  small  and  large 
intestine,  showing  the  transition  from  the  villus-covered  surface  of  the  former  to 
the  comparatively  smooth  surface  of  the  latter. 

To  show  Brunner's  glands  a  section  of  the  duodenum  is  required. 

To  show  the  varying  shapes  of  the  villi  in  the  different  regions,  sections  should 
also  be  made  of  the  jejunum  and  ileum. 

Solitary  follicles  may  usually  be  seen  in  any  of  the  above  sections. 

A  small  Peyer's patch,  together  with  the  entire  thickness  of  the  intestinal  wall, 
should  be  removed,  treated  as  above,  stained  with  haematoxylin-eosin  (technic  1, 
p.  16),  or  will)  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  16),  and  mounted  in 
balsam. 

(2)  A  vermiform  appendix,  as  fresh  as  possible,  should  be  cut  transversely  into 
small    pieces,   fixed- in    formalin-Midler's  fluid  (technic  5,  !»•   5),  and   hardened   in 


THE  DIGESTIVE  SYSTEM.  217 

alcohol.     Thin  transverse  sections  are  made  through  the  entire  wall,  stained  with 
haematoxylin-eosin  or  hasmatoxylin-picro-acid-fuchsin,  and  mounted  in  balsam. 

(3)  Fat  Absorption.— For  the  purpose  of  studying  the  process  by  which  fat 
passes  from  the  lumen  of  the  gut  into  the  chyle  vessels,  an  animal  should  be  killed 
at  the  height  of  fat  absorption.  A  frog  fed  with  fat  bacon  and  killed  two  days 
later,  a  dog  fed  with  fat  meat,  or  a  cat  with  cream  and  killed  after  from  four  to 
eight  hours,  furnishes  good  material.  Usually  if  the  preparation  is  to  be  successful, 
the  lumen  of  the  intestine  will  be  found  to  contain  emulsified  fat  and  the  lacteals  of 
the  mesentery  are  seen  distended  with  chyle.  Extremely  thin  slices  of  the  mucous 
membrane  of  the  small  intestine  are  fixed  in  i-per-cent  osmic  acid  or  in  osmium 
bichromate  solution  (5-per-cent  aqueous  solution  potassium  bichromate  and  2-per- 
cent aqueous  solution  osmic  acid— equal  parts)  for  twelve  to  twenty-four  hours, 
after  which  they  are  passed  rather  quickly  through  graded  alcohols.  Sections 
should  be  thin  and  mounted,  either  unstained  or  after  a  slight  eosin  stain,  in 
glycerin. 

(4)  The  blood-vessels  of  the  stomach  are  best  studied  in  injected  specimens. 
(See  page  20.) 

The  Larger  Glands  of  the  Digestive  System. 

The  smaller  tubular  glands  which  form  a  part  of  the  mucous 
membrane  and  submucosa  of  the  alimentary  tract  have  been  already 
described.  Certain  larger  glandular  structures,  the  development  of 
which  is  similar  to  that  of  the  smaller  tubules  but  which  come  to  lie 
wholly  without  the  alimentary  tract,  connected  with  it  only  by  their 
main  excretory  ducts,  and  which  are  yet  functionally  an  important 
part  of  the  digestive  system,  remain  to  be  considered. 
These  are 


(a)  The  parotid. 

1.  The  salivary  glands     j  (/;)  The  sublingual. 

J  (r)   The  submaxillary. 

2.  The  pancreas. 

3.  The  liver. 

1.  The   Salivary   Glands. 

The  salivary  glands  are  all  compound  tubular  glands.  In  man 
the  parotid  is  serous;  the  sublingual  and  submaxillary,  mixed  serous 
and  mucous  (page  177).  Only  the  general  structure  of  these  glands 
is  here  described,  the  minute 'structure  of  mucous  and  serous  glands 
having  been  described  on  page  177. 

Each  gland  consists  of  gland  tissue  proper  and  of  a  supporting 
connective-tissue  framework.  The  framework  consists  of  a  connec- 
tive-tissue capsule  which   encloses  the  gland,  but   blends   externally 


218 


THE   ORGANS. 


with  and  attaches  the  gland  to  the  surrounding  structures.  From 
the  capsule  trabecules  pass  into  the  gland,  subdividing  it  into  lobes 
and  lobules.  The  gland  tissue  proper  consists  of  systems  of  excretory 
ducts  opening  into  secretory  tubules,  all  being  lined  with  one  or  more 
layers  of  epithelial  cells.  Each  gland  has  one  main  excretory  duct. 
This  divides  into  branches — interlobar  ducts — which  run  to  the  lobes 
in  the  connective  tissue  which  separates  them.  The  interlobar  ducts 
give  rise  to  branches  which,  as  they  pass  to  the  lobules  in  the  inter- 


Fig.  134.— Diagrams  to  illustrate  the  Structure  of  the  Salivary  Glands.  (Stohr.)  A,  Parotid  ; 
B,  sublingual  ;  C\  submaxillary,  a,  Excretory  duct;  b,  secreting  tubule;  c,  intermediate 
tubule;  d.  terminal  tubule. 

lobular  connective  tissue,  are  known  as  interlobular  duets.  From 
the  latter,  branches  enter  the  lobules — intralobular  ducts — and  split 
up  into  terminal  secreting  tubules  which  constitute  the  bulk  of  the 
lobule.  From  the  interlobular  connective  tissue  delicate  extensions 
pass  into  the  lobules,  separating  the  gland  tubules.  The  glandular 
tissue  is  known  as  the  parenchyma  of  the  gland  in  contradistinction 
to  the  connective  or  interstitial  tissue. 

The  parotid  gland  in  man,  dog,  cat,  and  rabbit  is  a  purely 
serous  gland.  Its  duet  system  is  complex.  The  main  excretory 
duct  (Stenoni)  is  lined  by  two  layers  of  columnar  epithelium  resting 
upon  a  distinct  basement  membrane.  The  main  duct  divides  into 
numerous  branches,  which  in  turn  give  rise  to  so-called  secreting  or 
salivary  tubules.      These   are    continuous   with    long    narrow    inter- 


THE  DIGESTIVE  SYSTEM.  219 

mediate  tubules,  from  each  of  which  are  given  off  a  number  of  short 
terminal  tubules  (Fig.  134,  A).  The  two-layered  epithelium  of  the 
main  duct  becomes  reduced  in  the  smaller  ducts  to  a  single  layer  of 
columnar  cells.  The  salivary  tubules  are  lined  with  high  columnar 
epithelium,  the  bases  of  the  cells  showing  distinct  longitudinal  stri- 
ations.  In  the  intermediate  tubule  the  epithelium  is  flat,  sometimes 
spindle-shaped.  The  terminal  tubules  are  lined  with  serous  cells 
(page  177). 

The  sublingual  gland  is  a  mixed  gland  in  man,  dog,  cat,  and 
rabbit.  The  duct  system  is  less  complex  than  in  the  parotid.  The 
main  duct  (Bartholini)  sends  off  branches  which  are  continuous  with 
tubules,  showing  a  few  secretory  mucous  cells.  These  open  directly 
into  the  terminal  tubules  (Fig.  134,  B).  The  excretory  duct  is  like 
that  of  the  parotid  gland,  lined  with  a  two-layered  columnar  epithe- 
lium resting  upon  a  basement  membrane.  In  the  smaller  ducts  the 
epithelium  is  reduced  to  a  single  layer  of  columnar  cells.  There  are 
no  intermediate  tubules.  The  terminal  tubules  are  lined  with  both 
serous  and  mucous  cells  (page  177).  The  crescents  of  Gianuzzi 
(page  178)  are  numerous  and  large.  The  connective  tissue  of  the 
gland  contains  many  lymphoid  cells. 

The  submaxillary  gland  is  also  a  mixed  gland  in  man,  dog,  cat, 
and  rabbit.  In  complexity  of  its  duct  system  it  stands  between  the 
parotid  and  the  sublingual  (Fig.  134).  The  main  duct  (Wharton's) 
has  not  only  a  two-layered  epithelial  lining  resting  upon  a  basement 
membrane,  but  is  distinguished  by  a  richly  cellular  stroma  and  a  thin 
layer  of  longitudinally  disposed  smooth  muscle.  Branches  of  the 
main  duct  open  into  long  secretory  tubules  which  communicate  with 
the  terminal  tubules  by  means  of  short  narrow  intermediate  tubules 
(Fig.  1  34,  C).  The  secretory  tubules  are  lined  as  in  the  parotid  with 
columnar  cells  whose  bases  are  longitudinally  striated.  These  cells 
usually  contain  more  or  less  yellow  pigment.  The  intermediate 
tubules  have  a  low  cuboidal  or  flat  epithelium.  Most  of  the  end 
tubules  contain  serous  cells  only  (page  177).  The  crescents  of  the 
mucous  tubules  (page  178)  are  less  numerous  and  smaller  than  those 
in  the  sublingual,  consisting  as  a  rule  of  only  from  one  to  three  cells 

(Fig-  135)- 

Blood-vessels. — The  larger  arteries  run  in  the  connective-tissue 
septa  with  the  ducts,  giving  off  branches  which  accompany  the 
divisions  of  the  ducts  to  the  lobules,  where  they  break  up  into  capil- 


220 


THE  ORGANS. 


lary  networks  among  the  tubules.  These  give  rise  to  veins  which 
accompany  the  arteries. 

The  lymphatics  begin  as  minute  capillaries  in  the  connective  tis- 
sue separating  the  terminal  tubules.  These  empty  into  larger  lymph 
vessels  which  accompany  the  arteries  in  the  septa. 

The  nerves  of  the  salivary  glands  are  derived  from  both  cerebro- 
spinal and  sympathetic  systems,  consisting  of  both  medullated  and 
non-medullated  fibres.     The  medullated  fibres  are  afferent,  probably 


s  f  e 

FIG.  135. —Section  of  Human  Submaxillar}'  Gland.  X  252.  (Stohr.)  a,  Mucous  tubule  ;  /',  se- 
rous tubule  ;  c,  intermediate  tubule  ;  d,  "secretory"  tubule  ;  e,  demilune  ;  j\  lumen  ;  g, 
interstitial  connective  tissue. 

the  dendrites  of  cells  located  in  the  geniculate  ganglion.  Small 
bundles  of  these  fibres  accompany  the  ducts.  Single  fibres  leave  the 
bundles,  lose  their  medullary  sheaths,  and  form  a  non-medullated 
subepithelial  plexus,  from  which  delicate  fibrils  pass  to  end  freely 
among  the  epithelial  cells.  Efferent  impulses  reach  the  gland  through 
the  sympathetic.  The  fibres  arc  axones  of  cells  situated  in  small 
peripheral  ganglia;  the  cells  sending  axones  to  the  submaxillary 
lying  upon  the  main  excretory  duct  and  some  of  its  larger  branches ; 
those  sending  axones  to  the  sublingual  being  situated  in  a  small 
ganglion — the  sublingual — lying  in  the  triangular  area  bounded  by 
the  chorda  tympani,  the  lingual  nerve,  and  Wharton's  duct ;  those 
supplying  the  parotid  probably  being  in  the  otic  ganglion.  Axones 
from  these  cells  enter  the  glands  with  the  excretory  duct  and  follow 


THE  DIGES  TI VE  S  YS  TEM.  2  2  I 

its  branchings  to  the  terminal  tubules,  where  they  form  plexuses  be- 
neath the  epithelium.  From  these,  terminals  pass  to  the  secreting 
cells.  It  is  probable  that  the  salivary  glands  also  receive  sympa- 
thetic fibres  from  cells  of  the  superior  cervical  ganglia. 

TECHNIC. 

(i)  The  salivary  glands  should  be  fixed  in  Flemming's  fluid  (technic  7,  p.  6), 
or  in  formalin-Midler's  fluid  (technic  5,  p.  5).  Sections  are  cut  as  thin  as  possible, 
stained  with  haematoxylin-eosin  (technic  1,  p.  16),  and  mounted  in  balsam. 

(2)  For  the  study  of  the  secretory  activities  of  the  gland  cells,  glands  from  a 
fasting  animal  should  first  be  examined  and  then  compared  with  those  of  a  gland 
the  secretion  of  which  has  been  stimulated  by  the  subcutaneous  injection  of  pilo- 
carpine. Fix  in  Flemming's  or  in  Zenker's  fluid  (technic  9,  p.  6).  Examine  some 
sections  unstained  and  mounted  in  glycerin,  others  stained  with  haematoxylin-eosin 
and  mounted  in  balsam. 

(3)  The  finer  intercellular  and  intracellular  secretory  tubules  are  demon- 
strated by  Golgi's  method.  Small  pieces  of  absolutely  fresh  gland  are  placed  for 
three  days  in  osmium-bichromate  solution  (3-per-cent  potassium  bichromate  solu- 
tion, 4  volumes;  i-per-cent  osmic  acid,  1  volume),  and  then  transferred  without 
washing  to  a  0.75-per-cent  aqueous  solution  of  silver  nitrate.  Here  they  remain 
for  from  two  to  four  days,  the  solution  being  frequently  changed.  The  processes 
of  dehydrating  and  embedding  should  be  rapidly  done,  and  sections  mounted  in 
glycerin,  or,  after  clearing  in  xylol,  in  hard  balsam. 

Pancreas. 

The  pancreas  is  a  compound  tubular  gland.  While  in  general 
similar  to  the  salivary  glands,  it  has  a  somewhat  more  complicated 
structure.  A  connective-tissue  capsule  surrounds  the  gland  and 
gives  off  trabeculae,  which  pass  into  the  organ  and  divide  it  into 
lobules. 

In  some  of  the  lower  animals,  as  for  example  the  cat,  these 
lobules  are  well  defined,  being  completely  separated  from  one  another 
by  connective  tissue.  In  this  respect  they  resemble  the  lobules  of 
the  pig's  liver.  A  number  of  these  primary  lobules  are  grouped 
together  and  surrounded  by  connective  tissue,  which  is  considerably 
broader  and  looser  in  structure  than  that  separating  the  primary 
lobules.      These  constitute  a  lobule  group  or  secondary  lobule. 

In  the  human  pancreas  the  division  into  lobules  and  lobule  groups 
is  much  less  distinct,  although  it  can  usually  be  made  out.  This  is 
due  to  the  incompleteness  of  the  connective-tissue  septa,  the  human 
pancreas  in  this  respect  resembling  the  human  liver.  Rarely  the 
human  pancreas  is  distinctly  lobulated. 


THE   ORGANS. 


The  gland  has  a  main  excretory  duct,  the  pancreatic  duct  or 
duct  of  IVirsuug.  In  many  cases  there  is  also  a  secondary  excretory 
duct,  the  accessory  pancreatic    duct    or   duct   of  Santorini.      Both 

open  into  the  duodenum.  The  main  duct 
extends  almost  the  entire  length  of  the 
gland,  giving  off  short  lateral  branches,  one 
of  which  enters  the  centre  of  each  lobule 
group.  Here  it  splits  up  into  branches 
which  pass  to  the  primary  lobules.  From 
these  intralobular  ducts,  are  given  off 
long,  narrow,  intermediate  tubules,  which 
in  turn  give  rise  to  the  terminal  secreting 
tubules  (Fig.  136). 

The  excretory  ducts  are  lined  with  a 
simple  high  columnar  epithelium  which 
rests  upon  a  basement  membrane.  Outside 
of  this  is  a  connective-tissue  coat,  the  thick- 
ness of  which  is  directly  proportionate  to 
the  size  of  the  duct.  In  the  pancreatic 
duct  goblet  cells  are  present,  and  the  ac- 
companying connective  tissue  contains  small 
mucous  glands.  As  the  ducts  decrease 
in  size,  the  epithelium  becomes  lower  until 
the  intermediate  tubule  is  reached  where  it 
becomes  flat. 
The  terminal  tubules  themselves  are  most  of  them  very  short, 
frequently  almost  spherical.  This  and  the  fact  that  several  terminal 
tubules  are  given  off  from  the  end  of  each  intermediate  tubule  have 
led  to  the  description  of  these  tubules  as  alveoli,  and  of  the  pancreas 
as  a  tubulo-alveolar  gland,  although  there  is  no  dilatation  of  the 
lumen.  The  terminal  tubules  are  lined  with  an  irregularly  conical 
epithelium  resting  upon  a  basement  membrane  (Figs.  137  and  138). 
The  appearance  of  these  cells  depends  upon  their  functional  con- 
dition. Fach  cell  consists  of  a  central  zone  bordering  the  lumen, 
which  contains  numerous  granules  known  as  zymogen  granules,  and 
of  a  peripheral  zone  next  to  the  basement  membrane,  which  is  homo- 
geneous and  contains  the  nucleus  (Fig.  138).  The  relative  size  of 
these  zones  depends  upon  whether  the  cell  is  in  the  active  or  resting 
state  (compare  Fig.    1 39,  ^4   and   B).      During  rest  (fasting)  the  two 


Fig.  136.  —  Diagram  to  illus- 
trate Structure  of  Pancreas. 
(Stohr.)  a,  Excretory  duct ; 
b,  intermediate  tubule;  c,  c, 
terminal  tubules. 


THE  DIGESTIVE  SYSTEM. 


223 


zones  are  of  about  equal  size.      During  the  early  stages  of  activity 
(intestinal  digestion)   the  granules   largely  disappear  and  the  clear 


FIG.  137. — Section  of  Human  Pancreas.     X  112.     (KSlliker.)     ai\  Alveoli  ;  a,  interlobular  duct 
surrounded  by  interlobular  connective  tissue  ;  L,  islands  of  Langerhans  ;  v,  small  vein 

zone  occupies  almost  the  entire  cell.  During  the  height  of  digestion 
the  granules  are  increased  in  number,  while  after  prolonged  secre- 
tion they  are  again  almost  absent.  The  cell  now  returns  to  the  rest- 
ing state  in  which  the  two  zones  are  about  equal.  The  increase  and 
disappearance  of  the  granules  are  marked  by  the  appearance  of  the 
fluid  secretion  of  the  gland  in 
the  lumen.  It  would  thus 
seem  probable  that  the  zymo- 
gen granules  are  the  intracell- 
ular representatives  of  the 
secretion  of  the  gland. 

In  sections  of  the  gland 
there  are  seen  within  the  lu- 
mina  of  many  of  the  secreting 
tubules  one  or  more  small 
cells  of  which  little  but  the 
nucleus  can  usually  be  made 
out.  These  cells  lie  in  con- 
tact with  the  secreting  cells, 
and  resemble  the  flat  cells  which  line  the  intermediate  tubule. 
They  are  known  as  the  centro-acinar  {centro-tubular)  cells  of  Langer- 


FlG.  138.— From  Section  of  Human  Pancreas.  X 
700.  (Kolliker.)  a,  Gland  cell  ;  6,  basement  mem 
brane  ;  s,  intermediate  tubule;  c,  centroacinar 
cells  ;  sk,  intracellular  secretory  tubule. 


224 


THE   ORGANS. 


Iians  i  Fig.  138,  c).  Their  significance  is  not  definitely  known. 
Langerhans  considered  them  to  be  derived  from  the  intermediate  tub- 
ule, the  epithelium  of  which,  instead  of  directly  joining  that  of  the 


Flo.  139.— Sections  of  Alveoli  from  Rabbit's  Pancreas.  (Foster,  after  Kiihne  and  Lea.)  A, 
Resting  alveolus,  the  inner  zone  (a),  containing  zymogen  granules,  occupying  a  little 
more  of  the  cell  than  the  outer  clear  zone  (b)  ;  c,  indistinct  lumen.  B,  Active  alveolus, 
granules  coarser,  fewer,  and  confined  to  inner  ends  of  the  cell  (a),  the  outer  clear  zone  (/)) 
being  much  larger  ;  outlines  of  cells  and  of  lumen  much  more  distinct. 

terminal  tubule  as  in  the  submaxillary  gland,  was  continued  over 
into  the  lumen  of  the  terminal  tubule  (Fig.  138).  This  interpreta- 
tion has  been  quite  generally  accepted. 

Cells  which   differ  from  the   secreting  cells   are  frequently  found 


A  B 

FlO.  140  Sections  through  Alveoli  of  Human  Pancreas  Golgi  Method  (Dogiel),  to  show  in- 
tracellular secretory  tubules,  a,  Intermediate  tubule  giving  off  several  terminal  tubules, 
from  which  pass  off  minute  intracellular  secretory  tubules ;  b,  gland cellsliuing  terminal 
I  ubules. 

wedged  in   between  the  latter.      They  extend  from  the   lumen  to  the 
basement  membrane  and  are  probably  sustentacular. 

Passing    from    the     lumen    of    the    terminal    tubule,    sometimes 
between  the  centro-tubular  cells,  directly  into  the  cytoplasm  of  the 


THE  DIGESTIVE  SYSTEM.  225 

secreting  cells  are  minute  intracellular  secretory  tubules.      These  are 
demonstrable  only  by  special  methods  (Golgi)  (Fig.  140). 

The  pancreas  also  contains  peculiar  groups  of  cells,  the  cell-isl- 
ands of  LangerhaiiSyhaMmg  a  diameter  from  200  to  300  //.  (Figs.  137, 
141,  and  142).  The  "island"  cells  differ  quite  markedly  from  those 
which  line  the  terminal  tubules  (Fig.  141).  They  contain  no  zymo- 
gen granules.  Their  protoplasm  is  unstained  by  basic  dyes,  but 
stains  homogeneously  with  acid  dyes.     Their  nuclei  vary  greatly  in 


Fig.  141. — Island  of  Langerhans  and  few  surrounding  Pancreatic  Tubules.     (Bohm  and   von 
Davidoff.)     a,  Capillary  ;  b,  lumen  of  tubule. 

size,  some,  especially  where  the  cells  are  closely  packed,  being  small, 
others  being  large  and  vesicular.  Some  of  the  islands  are  quite 
sharply  outlined  by  delicate  fibrils  of  connective  tissue  (Fig.  141). 
Others  blend  with  the  surrounding  tissues. 

The  origin,  structure,  and  function  of  these  islands  have  been 
subjects  of  much  controversy.  For  some  time  they  were  considered 
of  lymphoid  origin.  They  are  now  believed  to  be  epithelial  cells 
having  a  developmental  history  similar  to  the  cells  lining  the  secret- 
ing tubules.  Each  cell-island  consists  of,  in  addition  to  the  cells,  a 
tuft  or  glomerulus  of  broad  tortuous  anastomosing  capillaries,  which 
arise  from  the  network  of  capillaries  which  surround  the  secreting 
15 


226 


THE   ORGANS. 


tubules.  The  close  relation  of  cells  and  capillaries  and  the  absence 
of  any  ducts  have  led  to  the  hypothesis  that  these  cells  furnish  a 
secretion — internal  secretion — which  passes  directly  into  the  blood- 
vessels. 

In  a  recent  publication  Opie  reviews  previous  work  upon  the  his- 
tology of  the  pancreas  and  adds  the  results  of  his  own  careful  re- 
searches.    He   concludes    that    the  cell-islands   of   Langerhans  are 


1 1  ®  ■ 


Fig.  142.—  From  Section  of  Pancreas,  the  blood-vessels  of  which  had  been  injected  (Kiihneand 
Lea),  showing  island  of  Langerhans  with  injected  blood-vessels,  surrounded  by  sections 
of  tubules.     Zymogen  granules  are  distinct  in  inner  ends  of  cells. 

definite  structures  "formed  in  embryologicai  life,"  that  "they 
possess  an  anatomical  identity  as  definite  as  the  glomeruli  of  the 
kidney  or  the  Malpighian  body  of  the  spleen,  and  that  they  subserve 
some  special  function."  He  calls  attention  to  the  similarity  which 
Schafer  noted  between  these  cell-islands  and  such  small  ductless 
structures  as  the  carotid  and  coccygeal  glands  and  the  parathyroid 
bodies.  From  his  study  of  the  pancreas  in  diabetes,  Opie  concludes 
that  the  islands  of  Langerhans  are  concerned  in  carbohydrate  me- 
tabolism. 

Blood-vessels. — The  arteries  enter  the  pancreas  with  the  main 
duct  and  break  up  into  smaller  arteries  which  accompany  the  smaller 
ducts.  These  end  in  a  capillary  network  among  the  secreting  tubules. 
From  this,  venous  radicles  arise  which  converge  to  form  larger  veins. 
These  pass  out  of  the  gland  in  company  with  the  arteries. 

Lymphatics. — Of  the  lymphatics  little  is  known. 

Nerves. — The  nerves  are  almost  wholly  from  the  sympathetic 
system,  and  are  non-medullated.  Some  of  them  are  axoncs  of  cells 
in  sympathetic  ganglia,  outside  the  pancreas;  others,  of  cells  situ- 
ated in  small  ganglia  within  the  substance  of  the  gland.      They  pass 


THE  DIGESTIVE  SYSTEM. 


'.  2  7 


to  plexuses  among  the  secreting  tubules,  to  which  and  to  the  walls  of 
the  vessels  they  send  delicate  terminal  fibrils. 

TECHNIC. 

(i)  The  general  technic  for  the  pancreas  is  the  same  as  for  the  salivary  glands 
(page  221). 

(2)  Zymogen  granules  may  be  demonstrated  by  fixation  in  formalin-Muller's 
fluid  (technic  5,  p.  5),  and  staining  with  picro-acid-fuchsin  (technic  2,  p.  16),  or  with 
Heidenhain's  iron  haematoxylin  (technic  3.  p.  14). 

(3)  The  arrangement  of  the  blood-vessels  in  the  islands  of  Langerhans  may  be 
studied  in  specimens  in  which  the  vascular  system  has  been  injected  (page  20). 


The    Liver. 

The  liver  is  a  compound  tubular  gland,  the  secreting  tubules  of 
which  anastomose.  There  are  thus,  strictly  speaking,  no  "  terminal 
tubules"  in  the  liver,  the  lumina  and  walls  of  neighboring  tubules 
anastomosing  without  any  distinct  line  of  demarcation. 


FlG.  143. — Section  of  Lobule  of  Pig's  Liver  X  60  (technic  1,  p.  234),  showing  lobule  completely 
surrounded  by  connective  tissue,  a.  Portal  vein  ;  /',  bile  duct  ;  t',  hepatic  artery  ;  J,  por- 
tal canal  ;  e,  capillaries  ;  _/",  central  vein  ;  ^,  cords  of  liver  cells  ;  //,  hepatic  vein. 

The  liver  is   surrounded   by  a  connective-tissue  capsule,  the  cap- 
sule of  Glisson.      At  the  hilum   this  capsule  extends   deep  into  the 


22  8  THE   ORGANS. 

substance   of   the    liver,  giving    off    broad    connective-tissue  septa, 
which  divide  the  organ  into  lobes.      From  the  capsule  and  from  these 
interlobar  septa,  trabecular  pass  into  the  lobes,  subdividing  them  into 
3  P    n 


-  ''•;■:>•  a 

M'^Wa 

K«] 

v-:  v. : 

Wu  H 

vm& 

■mm 


PIG     i  14. -Section  of  Human  Liver.     X  8o.     (Hendrickson.)     P,  Portal  vein;  H,  hepatic  ar- 
.   /'.   bile  duct.     I\  //,  B  constitute  the  portal  canal  and  lie  in  the  connective  tissue 
between  the  lobules. 

lobules.  In  some  animals,  as  for  example  the  pig,  each  lobule  is 
completely  invested  by  connective  tissue  (Fig.  143).  In  man,  only 
islands  of  connective  tissue  are  found,  usually  at  points  where  three 
or  more  lobules  meet  (Fig.  144).  The  lobules  are  cylindrical  or 
irregularly  polyhedral  in  shape,  about  1  mm.  in  breadth  and  2  mm. 
in  length.  Excepting  just  beneath  the  capsule,  where  they  are  fre- 
quently arranged  with  their  apices  toward  the  surface,  the  liver  lob- 
ules have  an  irregular  arrangement. 

The  lobule  (Fig.  143)  which  may  be  considered  the  anatomic 
unit  of  structure  of  the  liver,  consists  of  secreting  tubules  arranged 
in  a  definite  manner  relatively  to  the  blood-vessels.  The  blood-ves- 
sels of  the  liver  must  therefore  be  first  considered. 


THE  DIGESTIVE  SYSTEM. 


229 


The  blood  supply  of  the  liver  is  peculiar  in  that  in  addition  to 
the  ordinary  arterial  supply  and  venous  return,  which  all  organs  pos- 
sess, the  liver  receives  venous  blood  in  large  quantities  through  the 
portal  vein.  There  are  thus  two  afferent  vessels,  the  hepatic  artery 
and  the  portal  vein,  the  former  carrying  arterial  blood,  the  latter 
venous  blood  from  the  intestine.  Both  vessels  enter  the  liver  at  the 
hilum  and  divide  into  large  interlobar  branches,  which  follow  the 
connective-tissue  septa  between  the  lobes.  From  these  are  given  off 
interlobular  branches,  which  run  in  the  smaller  connective- tissue  septa 
between  the  lobules.  From  the  interlobular  branches  of  the  portal 
vein  arise  veins  which  are  still  interlobular  and  encircle  the  lobules. 
These  send  off  short  branches  which  pass  to  the  surface  of  the 
lobule,  where  they  break  up  into  a  rich  intralobular  capillary  net- 
work. These  intralobular  capillaries  all  converge  toward  the  centre 
of  the  lobule,  where  they  empty  into  the 
central  vein  (Fig.  143).  The  central 
veins  are  the  smallest  radicles  of  the 
hepatic  veins,  which  are  the  efferent  ves- 
sels of  the  liver.  Each  central  vein  be- 
gins at  the  apex  of  the  lobule  as  a  small 
vessel  little  larger  than  a  capillary.  As 
it  passes  through  the  centre  of  the  long 
axis  of  the  lobule  the  central  vein  con- 
stantly receives  capillaries  from  all  sides, 
and,  increasing  in  size,  leaves  the  lobule 
at  its  base.  Here  it  unites  with  the 
central  veins  of  other  lobules  to  form 
the  sublobular  vein  which  is  a  branch  of 
the  hepatic. 

The  hepatic  artery  accompanies  the 
portal  vein,  following  the  branchings  of 
the  latter  through  the  interlobar  and  in- 
terlobular connective  tissue,  where  its 
finer  twigs  break  up  into  capillary  net- 
works. Some  of  these  capillaries  empty 
into  the  smaller  branches  of  the  portal  vein  ;  others  enter  the  lobules 
and  anastomose  with  the  intralobular  portal  capillaries. 

The  main  excretory  duct — hepatic  duct — leaves  the  liver  at  the 
hilum    near   the   entrance  of    the    portal    vein    and    hepatic    artery. 


Fig.  145.  —  Portal  Canal.  X  315. 
(Klein  and  Smith.)  ■?,  Hepatic 
artery  ;  V,  portal  vein  ;  />,  bile 
duct. 


230  THE   ORGANS. 

Within  the  liver  the  duct  divides  and  subdivides,  giving  off  inter- 
lobar, and  these  in  turn  interlobular  branches.  These  ramify  in  the 
connective  tissue,  where  they  always  accompany  the  branches  of  the 
portal  vein  and  hepatic  artery.  These  three  structures — the  hepatic 
artery,  the  portal  vein,  and  the  bile  duct,  which  always  occur  together 
in  the  connective  tissue  which  marks  the  point  of  separation  of  three 
or  more  lobules — together  constitute  the  portal  canal  (Fig.  145). 
From  the   interlobular  ducts   short   branches   pass  to  the  surfaces  of 


?t*2 


m 


'§-> 


m 


- 


IXtO,  •    IS 


s 


9*   ( 

^'*r—.^ ^      ™  -■■■     "<v.--  '^  :f      , 

mi •  v^f0 "    ■•  ' - ; -:  — ^       <Mj    / 

^-.  '  •  -  \    / 


w$®m 


1 


FlG.  146. — Part  of  Lobule  of  Human   Liver,  showing  capillaries  and  anastomosing  cords  of 
liver  cells.     X  350.     a,  Liver  cells  ;  b.  capillaries. 

the  lobules.  From  these  are  given  off  extremely  narrow  tubules, 
which  enter  the  lobule  as  intralobular  secreting  tubules. 

The  walls  of  the  ducts  consist  of  a  single  layer  of  epithelial  cells 
resting  upon  a  basement  membrane  and  surrounded  by  connective 
tissue  (Fig!  145).  The  height  of  the  epithelium  and  the  amount  of 
connective  tissue  are  directly  proportionate  to  the  size  of  the  duct. 
In  the  largest  ducts  there  are  usually  a  few  scattered  smooth  muscle 
cells.  The  walls  of  the  secreting  tubules  are  formed  by  the  liver 
cells. 

The  liver  cells  (Fig.    146)  are  irregularly  polyhedral  in  shape. 


THE  DIGESTIVE  SYSTEM. 


231 


They  have  a  granular  protoplasm  which  frequently  contains  glycogen, 
pigment  granules,  and  droplets  of  fat  and  bile.  Each  cell  contains 
one  or  more  spherical  nuclei.      Like  other  gland  cells,  the  granularity 


FIG.  147.— Part  of  Lobule  of  Human  Liver,  Golgi  Method  (technic  3,  p.  234),  to  show  relations 
of  bile  duct  to  intralobular  secretory  tubuies  and  of  the  latter  to  the  liver  cells,  a,  Rile 
duct ;  d,  cords  of  liver  cells  ;  c.  blood  capillaries  ;  (/,  central  vein  ;  e,  secretory  tubules. 

of  the  protoplasm  depends  upon  its  functional  condition.  Within 
the  cells  are  minute  irregular  canals,  some  of  which  can  be  injected 
through  the  blood-vessels,  while  others  are  apparently  continuous 
with  the  secreting  tubules  (Fig.  148,  A  and  B). 

The  capillaries  of  the  portal  vein,  as  they  anastomose  and  con- 


A  B 

Fig.  14S. — A,  Cell  from  human  liver  showing1  intracellular  canals  (Browicz)  ;  c,  intracellular 
canal  ;  «,  nucleus.  />',  From  section  of  rabbit's  liver  injected  through  portal  vein,  show- 
ing; intracellular  canals  (continuous  with  intercellular  blood  capillaries).      (Schafer.) 

verge  from  the  periphery  to  the  centre  of  the  lobule,  form  long- 
meshed  capillary  networks.  In  the  meshes  of  this  network  lie  the 
anastomosing  secreting  tubules.      On  account   of  the  shape  of  the 


-o- 


THE   ORGANS. 


capillary  network,  the  liver  cells,  which  form  the  walls  of  these 
tubules,  are  arranged  in  anastomosing  rows  or  cords,  known  as  hepatic 
cords  or  cords  of  liver  cells  (Fig.  146). 

The  secreting  tubules  (Fig.  147)  are  extremely  minute  channels, 
the  walls  of  which  are  the  liver  cells.  A  secretory  tubule  always  runs 
between  two  contiguous  liver  cells,  in  each  of  which  a  groove  is  formed. 
The  blood  capillaries,  on  the  other  hand,  are  found  at  the  corners  where 


^*lfP 


Fig.  149.-  Liver  Lobule,  to  show  Connective-tissue  Framework.     (Mall.) 


three  or  more  liver  cells  come  in  contact.  It  thus  results  that  bile 
tubules  and  blood  capillaries  rarely  lie  in  contact,  but  are  regularly 
separated  by  part  of  a  liver  cell.  Exceptions  to  this  rule  sometimes 
occur.  While  most  of  the  secretory  tubules  anastomose,  some  of 
them  end  blindly  either  between  the  liver  cells  or,  in  some  instances, 
after  extending  a  short  distance  within  the  cell  protoplasm  (Fig. 
148,  A).  At  the  surface  of  the  lobule  there  is  a  modification  of 
some  of  the  liver  cells  to  a  low  cuboidal  type,  and  these  become  con- 
tinuous with  the  lining  cells  of  the  smallest  bile  ducts,  the  secretory 
tubule  being  continuous  with  the  duct  lumen. 


THE  DIGESTIVE  SYSTEM.  233 

Special  methods  of  technic  have  demonstrated  a  connective-tissue 
framework  within  the  lobule.  This  consists  of  a  reticulum  of  ex- 
tremely delicate  fibrils  which  envelop  the  capillary  blood-vessels,  and 
of  a  smaller  number  of  coarser  fibres  which  radiate  from  the  region 
of  the  central  vein — radiate  fibres  (Fig.  149). 

Special  technical  methods  also  show  the  presence  of  stellate  cells 
— cells  of  Kupffer — within  the  lobule.  These  are  interpreted  by 
Kupffer  as  belonging  to  the  endothelium  of  the  intralobular  capil- 
laries. 

Blood-vessels. — These  have  been  already  described. 

Lymph  vessels  form  a  network  in  the  liver  capsule.  These  com- 
municate with  deep  lymphatics  in  the  substance  of  the  organ.  The 
latter  accompany  the  portal  vein  and  follow  the  ramifications  of  its 
capillaries  within  the  lobule  as  far  as  the  central  vein. 

The  nerves  of  the  liver  are  mainly  non-medullated  axones  of 
sympathetic  neurones.  The  nerves  accompany  the  blood-vessels  and 
bile  ducts,  around  which  they  form  plexuses.  These  plexuses  give 
off  fibrils  which  end  on  the  blood-vessels,  bile  ducts,  and  liver  cells. 

Three  main  ducts,  all  parts  of  a  single  excretory  duct  system,  are 
concerned  in  the  transportation  of  the  bile  to  the  intestine,  the  he- 
patic, the  cystic,  and  the  common.  Their  walls  consist  of  a  mucous 
membrane,  a  submucosa,  and  a  layer  of  smooth  muscle.  The  mucosa 
is  composed  of  a  simple  columnar  epithelium  resting  upon  a  base- 
ment membrane  and  a  stroma  which  contains  smooth  muscle  cells 
and  small  mucous  glands.  The  submucosa  is  a  narrow  layer  of  con- 
nective tissue.  Hendrickson  describes  the  muscular  coat  as  consist- 
ing of  three  layers,  an  inner  circular,  a  middle  longitudinal,  and  an 
external  oblique.  At  the  entrance  of  the  common  bile  duct  into  the 
intestine,  and  at  the  junction  of  the  duct  of  Wirsung  with  the  com- 
mon duct,  there  are  thickenings  of  the  circular  fibres  to  form  sphinc- 
ters. In  the  cystic  duct  occur  folds  of  the  mucosa — the  Heist erian 
valve — into  which  the  muscularis  extends. 

The  Gall-Bladder. 

The  wall  of  the  gall-bladder  consists  of  three  coats — mucous, 
muscular,  and  serous. 

The  mucous  membrane  is  thrown  up  into  small  folds  or  ruga, 
which  anastomose  and  give  the  mucous  surface  a  reticular  appear- 


234  THE   ORGANS. 

ance.  The  epithelium  is  of  the  simple  columnar  variety  with  nuclei 
situated  at  the  basal  ends  of  the  cells.  A  few  mucous  glands  are 
usually  found  in  the  stroma. 

The  muscular  coat  consists  of  bundles  of  smooth  muscle  cells 
which  are  disposed  in  a  very  irregular  manner,  and  are  separated  by 
considerable  fibrous  tissue.  A  richly  vascular  layer  just  beneath  the 
stroma  is  almost  free  from  muscle  and  corresponds  to  a  submucosa. 
It  frequently  contains  small  lymph  nodules. 

The  serous  coat  is  a  reflection  of  the  peritoneum. 

TECHNIC. 

(i)  Before  taking  up  the  study  of  the  human  liver,  the  liver  from  one  of  the 
lower  animals  in  which  each  lobule  is  completely  surrounded  by  connective  tissue 
should  be  studied.  Fix  small  pieces  of  a  pig's  liver  in  formalin-Muller's  fluid 
(technic  5.  p.  5).  Cut  sections  near  and  parallel  to  the  surface.  Stain  with  hae- 
matoxylin-picro-acid-fuchsin  (technic  3,  p.  16)  and  mount  in  balsam.  In  the  pig's 
liver  the  lobules  are  completely  outlined  by  connective  tissue  and  the  yellow  picric- 
acid-stained  lobules  are  in  sharp  contrast  with  the  red  fuchsin-stained  connective 
tissue. 

!  2 1  For  the  study  of  the  human  liver  treat  small  pieces  of  perfectly  fresh  tissue 
in  the  same  manner  as  the  preceding,  but  stain  with  haematoxylin-eosin  (technic  1, 
p.  16  . 

(3)  The  secretory  tubules  and  smaller  bile  ducts  may  be  demonstrated  by 
technic  4.  p.  23.     A  light  eosin  stain  brings  out  the  liver  cells. 

(4)  For  the  study  of  the  blood-vessels  of  the  liver,  inject  the  vessels  through 
the  inferior  vena  cava  or  portal  vein.  If  the  vena  cava  is  used,  it  is  convenient  to 
inject  from  the  heart  directly  through  the  right  auricle  into  the  vena  cava.  Sec- 
tions should  be  rather  thick  and  may  be  stained  with  eosin,  or  even  lightly  with 
ha-matoxylin-eosin  (technic  1.  p.  16).  and  mounted  in  balsam. 

<ji  For  demonstrating  the  intralobular  connective  tissue  Oppel  recommends 
fixing  fresh  tissue  in  alcohol,  placing  for  twenty-four  hours  in  a  0.5-per-cent  aqueous 
solution  of  yellow  chromate  of  potassium,  washing  in  very  dilute  silver  nitrate 
solution  (a  leu  drops  of  0.75-per-cent  solution  to  50  c.c.  of  water)  and  then  trans- 
ferring to  0.75-per-cent  silver  nitrate  solution,  where  it  remains  for  twenty-four 
hours.  Embed  quickly  in  celloidin.  The  best  tissue  is  usually  found  near  the 
surfaces  of  the  blocks.  A  similar  result  is  obtained  by  fixing  fresh  tissue  in  0.5- 
per-cent  chromic-acid  solution  for  three  days,  then  transferring  to  0.5-pcr-cent  sil- 
ver nitrate  solution  lor  two  days. 

Development  of  the  Digestive  System. 

In  the  development  of  the  digestive  system  all  the  layers  of  the 
blastoderm  arc  involved.  Mesoderm  and  entoderm  are,  however,  the 
layers  most  concerned,  as  the  ectoderm  is  used  only  in  the  formation 
of  the  oral  and  anal  orifices.  The  primitive  alimentary  canal  is 
formed  by  two   folds  which   grow  out  from  the  ventral  surface  of  the 


THE  DIGESTIVE  SYSTLM  235 

embryo  and  unite  to  form  a  canal,  in  a  manner  quite  similar  to  the 
formation  of  the  neural  canal  (page  332).  In  this  way  the  primitive 
gut  is  lined  with  cells  which  previously  formed  the  ventral  surface 
of  the  embryo,  i.e.,  entoderm.  A  portion  of  the  mesoderm  accom- 
panies the  entoderm  in  the  formation  of  the  folds.  This  is  known 
as  the  visceral  layer  of  the  mesoderm.  The  primary  gut  is  thus  a 
closed  sac  or  tube.  It  is  connected  with  the  umbilical  vesicle,  but 
has  no  connection  with  the  exterior.  These  connections  are  formed 
later  by  oral  and  anal  invaginations  of  ectoderm  which  extend  in- 
ward and  open  up  into  the  ends  of  the  hitherto  imperforate  gut.  The 
ends  of  the  alimentary  tract,  including  the  oral  cavity  and  all  of  the 
glands  and  other  structures  connected  with  it,  are  of  ectodermic 
origin.  The  epithelial  lining  of  the  gut  and  the  parenchyma  of  all 
glands  connected  with  it  are  derived  from  entoderm.  The  muscle, 
the  connective  tissue,  and  the  mesothelium  of  the  serosa  are  de- 
veloped from  mesoderm. 

The  mesodermic  elements  show  little  variation  throughout  the 
gut,  the  peculiarities  of  the  several  anatomical  divisions  of  the  latter 
being  dependent  mainly  on  special  differentiation  of  the  entoderm 
(epithelium).  Beneath  the  entodermic  cells  is  a  narrow  layer  of 
loosely  arranged  tissue  which  later  separates  into  stroma,  muscularis 
mucosae,  and  submucosa.  Outside  of  this  a  broader  mesodermic 
band  of  firmer  structure  represents  the  future  muscularis. 

The  stomach  first  appears  as  a  spindle-shaped  dilatation  about  the 
end  of  the  first  month.  Its  entodermic  cells,  which  had  consisted  of 
a  single  layer,  increase  in  number  and  arrange  themselves  in  short 
cylindrical  groups.  These  are  the  first  traces  of  tubular  glands. 
They  increase  in  length  and  extend  downward  into  the  mesodermic 
tissue.  For  a  time  the  cells  lining  the  peptic  glands  are  all  appar- 
ently alike,  but  at  about  the  fourth  month  the  differentiation  into 
chief  cells  and  parietal  cells  takes  place. 

In  the  intestines  a  proliferation  of  the  epithelium  and  of  the 
underlying  stroma  results  in  the  formation  of  villi.  These  appear 
about  the  tenth  week,  in  both  small  and  large  intestines.  In  the 
former  they  increase  in  size,  while  in  the  latter  they  atrophy  and 
ultimately  disappear.  The  simple  tubular  glands  of  the  intestines 
develop  in  a  manner  similar  to  those  of  the  stomach. 

The  mesothelium  of  the  serosa  is  derived  from  the  mesodermic 
cells  of  the  primitive  body  cavity. 


236  THE   ORGANS. 

The  development  of  the  larger  glands,  connected  with  the  diges- 
tive tract,  takes  place  in  a  manner  similar  to  the  formation  of  the 
simple  tubular  glands.  All  originate  in  extensions  downward  of 
entodermic  cords  into  the  underlying  mesodermic  tissue.  From  the 
lower  ends  of  these  cords,  branches  extend  in  all  directions  to  form 
the  complex  systems  of  tubules  found  in  the  compound  glands. 

The  salivary  glands  being  developed  from  the  oral  cavity,  origi- 
nate in  similar  invaginations  of  ectodermic  tissue. 

In  the  case  of  the  pancreas  a  portion  of  the  gland  has  an  inde- 
pendent origin  in  the  epithelium  of  the  ductus  choledochus.  This 
portion  ultimately  unites  with  the  main  mass  of  the  gland  and  its 
duct.  The  duct  of  Santorini  sometimes  remains  patent,  but  in  many 
cases  atrophies  so  that  the  entire  pancreatic  secretion  usually  reaches 
the  intestine  through  the  pancreatic  duct. 

The  liver  begins  as  a  ventral  downgrowth  of  the  intestinal  epi- 
thelium into  the  mesoderm  of  the  transverse  septum.  This  almost 
immediately  divides  into  two  hepatic  diverticula.  About  the  ends 
of  these  diverticula  active  proliferation  of  entodermic  cells  takes 
place,  and  this  represents  the  first  appearance  of  liver  tissue. 

General  References  for  Further  Study. 

Oppel :  Lehrbuch  der  vergleichenden  mikroskopischen  Anatomic 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 

Opie  :  The  Pancreas. 

Stohr:  Salivary  Glands,  in  Text-book  of  Histology. 


CHAPTER    VII. 
THE    RESPIRATORY   SYSTEM. 

The  respiratory  apparatus  consists  of  a  system  of  passages — 
nares,  larynx,  trachea,  and  bronchi,  which  serve  for  the  transmission 
of  air  to  and  from  the  essential  organ  of  respiration,  the  lungs. 

The   Nares. 

The  nares,  or  nasal  passages,  are  divided  into  vestibular,  respira- 
tory, and  olfactory  regions,  the  differentiation  depending  mainly  upon 
the  structure  of  their  mucous  membranes. 

The  vestibular  region  marks  the  transition  between  skin  and 
mucous  membrane  (page  176).  Its  epithelium  is  of  the  stratified 
squamous  variety  and  rests  upon  a  basement  membrane,  which  is 
thrown  into  folds  by  papillae  of  the  underlying  stroma.  The  latter 
is  richly  cellular  and  contains  sebaceous  glands  (page  322)  and  the 
follicles  of  the  nasal  hairs. 

The  respiratory  region  is  much  larger  than  both  the  vestibular 
and  olfactory  regions.  Its  epithelium  is  of  the  stratified  columnar 
variety.  The  cells  of  the  surface  layer  are  ciliated  and  are  inter- 
spersed with  goblet  cells.  The  stroma  is  distinguished  by  its  thick- 
ness (3  to  5  mm.  over  the  inferior  turbinates)  and  by  the  presence  of 
networks  of  such  large  veins  that  the  tissue  closely  resembles  erectile 
tissue.  It  contains  considerable  diffuse  lymphoid  tissue  and  here 
and  there  small  lymph  nodules.  In  the  stroma  are  small  simple 
tubular  glands  lined  with  both  serous  and  mucous  cells.  There  is 
no  submucosa,  the  stroma  being  connected  directly  with  the  perios- 
teum and  perichondrium  of  the  nasal  bones  and  cartilages. 

The  mucous  membrane  of  the  accessory  nasal  sinuses  is  similar  in 
structure  to  that  of  the  respiratory  region  of  the  nares,  but  is  thinner 
and  contains  fewer  glands. 

The  olfactory  region  can  be  distinguished  with  the  naked  eye 
by  its  brownish -yellow  color,  in  contrast  with  the  reddish  tint  of  the 
surrounding  respiratory  mucosa.  The  epithelium  is  of  the  stratified 
columnar  type,  and  is  considerably  thicker  than  that  of  the  respiratory 

237 


238  THE   ORGANS. 

region.     The  surface  cells  are  of  two  kinds:  (1)  sustentacular  cells, 
and  12)  olfactory  cells. 

(1)  The  sustentacular  cells  are  the  more  numerous.  Each  cell 
consists  of  three  parts  :  (/?)  A  superficial  portion,  which  is  broad  and 
cylindrical,  and  contains  pigment,  and  granules  arranged  in  longi- 
tudinal rows.  The  cells  have  well-marked,  striated,  thickened  free 
borders,  which  unite  to  form  the  so-called  membrana  limit ans  olfac- 
toria.  (/>)  A  middle  portion  which  contains  an  oval  nucleus.  As 
the  nuclei  of  these  cells  all  lie  in  the  same  plane,  they  form  a  distinct 
narrow  band,  which  is  known  as  the  zone  of  oval  nuclei.  (c)  A  thin 
filamentous  process  which  extends  from  the  nuclear  portion  down 
between  the  cells  of  the  deeper  layers.  This  process  is  irregular  and 
pitted  by  pressure  of  surrounding  cells.  It  usually  forks  and  appar- 
ently anastomoses  with  processes  of  other  cells  to  form  a  sort  of  pro- 
toplasmic reticulum. 

(2)  The  olfactory  cells  lie  between  the  sustentacular  cells.  Their 
nuclei  are  spherical,  lie  at  different  levels,  and  are  most  of  them  more 
deeply  placed  than- those  of  the  sustentacular  cells.  They  thus  form 
a  broad  band,  the  zone  of  round  nuclei.  From  the  nuclear  portion 
of  the  cell  a  delicate  process  extends  to  the  surface,  where  it  ends  in 
several  minute  hair-like  processes.  From  the  opposite  pole  of  the 
cell  a  longer  process  extends  centrally  as  a  centripetal  nerve  fibre. 
The  olfactory  cell  is  thus  seen  to  be  of  the  nature  of  a  ganglion  cell 
(see  also  page  446). 

Between  the  nuclear  parts  of  the  olfactory  cells  and  the  basement 
membrane  are  the  basal  cells.  These  are  small  nucleated  elements, 
the  irregular  branching  protoplasm  of  which  anastomoses  with  that 
of  neighboring  basal  cells  and  of  the  sustentacular  cells  to  form  the 
peculiar  protoplasmic  reticulum  already  mentioned. 

The  basement  membrane  is  not  well  developed. 

The  stroma  consists  of  loosely  arranged  white  fibres,  delicate  elas- 
tic fibres,  and  connective-tissue  cells.  Embedded  in  the  stroma  are 
large  numbers  of  simple  branched  tubular  glands,  the  glands  of  How- 
man.  Each  tubule  consists  of  a  duct,  a  body,  and  a  fundus.  The 
secreting  cells  are  large  and  irregular  and  contain  a  yellowish  pig- 
ment, which  with  that  of  the  sustentacular  cells  is  responsible  for 
the  peculiar  color  of  the  olfactory  mucosa.  These  glands  were  long 
described  as  serous,  but  are  now  believed  to  be  mucous  in  character. 
They  frequently  extend  beyond  the  limits  of  the  olfactory  region. 


THE  RESPIRATORY  SYSTEM.  239 

The    Larynx. 

The  larynx  consists  essentially  of  a  group  of  cartilages  united  by 
strong  fibrous  bands  and  lined  by  mucous  membrane. 

The  epithelium  covering  the  true  vocal  cords,  the  free  margin  of 
the  epiglottis,  and  parts  of  the  arytenoid  cartilages  is  of  the  stratified 
squamous  variety  with  underlying  papillae.  With  these  exceptions 
the  mucous  membrane  of  the  larynx  is  lined  with  stratified  columnar 
ciliated  epithelium  similar  to  that  of  the  respiratory  portion  of  the 
nares.  Numerous  goblet  cells  are  usually  present,  and  the  epithe- 
lium rests  upon  a  broad  basement  membrane.  On  the  posterior  sur- 
face of  the  epiglottis  many  taste  buds  (see  nerve  endings,  page  349) 
are  embedded  in  the  epithelium. 

The  stroma  is  especially  rich  in  elastic  fibres.  The  true  vocal 
cords  consist  almost  wholly  of  longitudinal  elastic  fibres  covered  by 
stratified  squamous  epithelium.  Lymphoid  cells  are  present  in  vary- 
ing numbers.  In  some  places  they  are  so  numerous  that  the  tissue 
assumes  the  character  of  diffuse  lymphoid  tissue.  Distinct  nodules 
sometimes  occur. 

Owing  to  the  absence  of  a  muscularis  mucosas  the  stroma  passes 
over  with  no  distinct  line  of  demarcation  into  the  submucosa.  This 
is  a  more  loosely  arranged,  less  cellular  connective  tissue,  and  con- 
tains simple  tubular  glands  lined  with  both  serous  and  mucous  cells. 

Externally  the  submucosa  merges  into  a  layer  of  more  dense 
fibrous  tissue  which  connects  it  with  the  laryngeal  cartilages  and  with 
the  surrounding  structures.  Immediately  surrounding  the  cartilages 
the  connective  tissue  forms  an  extremely  dense  layer,  the  perichon- 
drium. 

Of  the  cartilages  of  the  larynx,  the  epiglottis,  the  middle  part  of 
the  thyroid,  the  apex  and  vocal  process  of  the  arytenoid,  the  carti- 
lages of  Santorini  and  of  Wrisburg  are  of  the  yellow  elastic  variety. 
The  main  body  of  the  arytenoid,  the  rest  of  the  thyroid  and  the  cri- 
coid cartilages  are  hyaline.  After  the  twentieth  year,  more  or  less 
ossification  is  usually  found  in  the  cricoid  and  thyroid  cartilages. 

The   Trachea. 

The  walls  of  the  trachea  consist  of  three  layers — mucosa,  submu- 
cosa, and  fibrosa  (Fig.    150). 

The  mucosa  is  continuous  with  that  of  the  larynx,  which  it  close- 


240 


THE   ORGANS. 


ly  resembles  in  structure.  It  consists  of  a  stratified  columnar  ciliated 
epithelium,  with  numerous  goblet  cells,  resting  upon  a  broad  base- 
ment membrane,  and  of  a  stroma  of  mixed  fibrous  and  elastic  tissue 
containing  many  lymphoid  cells. 

The  submucosa  is  not  distinctly  marked  off  from  the  stroma  on 
account  of  the  absence  of  a  muscularis  mucosae.  It  is  distinguished 
from  the  stroma  by  its  looser,  less  cellular  structure,  by  its  numerous 
large  blood-vessels,  and  by  the  presence  of  glands.  These  are  of  the 
simple  branched  tubular  variety  and  are  lined  with  both  serous  and 
mucous  cells.  Some  of  the  mucous  tubules  have  well-marked  cres- 
cents of  Gianuzzi.  The  glands  are  most  numerous  between  the  ends 
of  the  cartilaginous  rings,  where  they  extend  into  the  fibrosa. 

The  fibrosa  is  composed  of  coarse,  rather  loosely  woven  connec- 
tive-tissue  fibres   embedded   in    which   are   the    trachea!  cartilages. 


'■"-'■-''■ -.^ 


'  .  1  ' 


FIG.  i;o. — From  Longitudinal  Section  of  Human  Trachea,  x  40.  (Technic  3,  p.  242.)  a,  Epi- 
thelium; /',  stroma;  c,  cartilage;  </.  fibrous  coat;  e,  serous  iubules;y,  mucous  tubules; 
4',  glands  in  submucosa  ;  //,  ducts. 


These  are  incomplete  rings  of  hyaline  cartilage  shaped  like  the  letter 
C  (Fig.  151).  They  are  from  sixteen  to  twenty  in  number  and  en- 
circle about   four-fifths   of   tht:   tube,  being   open    posteriorly.     The 


THE  RESPIRATORY  SYSTEM. 


241 


openings  between  the  ends  of  the  cartilaginous  rings  are  bridged  over 
by  a  thickened  continuation  of  the  fibrous  coat,  strengthened  by  a 
layer  of  smooth  muscle  (Fig.  151,  m).     The  bundles  of  muscle  cells 


-  -:M  / 


PlG.  151.— Transverse  Section  of  Human  Trachea  through  One  of  the  Cartilage  Rings.  X  8. 
(Kolliker.)  E,  Epithelium  of  (5)  mucous  membrane  ;  dr,  glands  ;  as,  gland  duct ;  ad,  ade- 
noid tissue  ;  A",  cartilage  ;  m.  smooth  muscle  cut  longitudinally,  extending  across  between 
ends  of  cartilage  ring. 


run  mainly  in  a  transverse  direction,  and  extend  across  the  intervals 
between  adjacent  rings  as  well  as  between  their  open  ends.  There 
are  frequently  a  few  bundles  of  longitudinally  disposed  cells. 

Outside  the  fibrous  coat  proper  is  a  looser,  more  irregular  con- 
nective tissue,  which  serves  to  attach  the  trachea  to  the  surrounding 
structures. 

Blood-vessels,  lymphatics,  and  nerves  have  a  similar  distribution 
in  larynx  and  trachea.  The  larger  vessels  pass  directly  to  the  sub- 
16 


242  THE   ORGANS. 

mucosa.  From  these,  smaller  branches  pass  to  the  different  coats, 
where  they  break  up  into  capillary  networks. 

Lymphatics  form  plexuses  in  the  submucosa  and  mucosa,  the  most 
superficial  lying  just  beneath  the  subepithelial  capillary  plexus. 

The  nerves  of  the  larynx  and  trachea  are  derived  from  both  cere- 
bro-spinal  and  sympathetic  systems.  The  cerebro-spinal  nerves  are 
afferent,  the  dendrites  of  spinal  ganglion  cells.  They  form  a  sub- 
epithelial plexus  from  which  are  given  off  fibrils  which  pass  into  the 
epithelium  and  terminate  freely  among  the  epithelial  cells.  Other 
afferent  fibres  of  cerebro-spinal  nerves  pass  to  the  muscular  coat  of 
the  trachea.  Sympathetic  nerve  fibres  form  plexuses  which  are 
interspersed  with  minute  groups  of  ganglion  cells.  Axones  from 
these  ganglion  cells  have  been  traced  to  the  smooth  muscle  cells  of 
the  trachea.  Sympathetic  axones  also  pass  to  the  glands  of  the 
trachea  and  larynx.  On  the  under  surface  of  the  epiglottis  small 
taste  buds  are  found. 

TECHNIC. 

(i)  For  the  study  of  the  details  of  structure  of  the  walls  of  the  nares  and  larynx, 
fix  small  pieces  of  perfectly  fresh  material  from  different  regions  in  formalin -Mtil- 
ler's  fluid  (technic  5,  p.  5),  harden  in  alcohol,  stain  sections  with  haematoxylin- 
eosin  (technic  1,  p.  16),  and  mount  in  balsam. 

(2)  The  general  relations  of  the  parts  can  be  studied  by  removing  the  larynx, 
upper  part  of  the  trachea,  and  corresponding  portion  of  the  oesophagus  of  an  ani- 
mal or  of  a  new-born  child,  fixing  and  hardening  as  above,  and  cutting  longitudinal 
sections  through  the  entire  specimen. 

(3)  Trachea..— Remove  a  portion  of  the  trachea  and  treat  as  in  technic  (1). 
Both  longitudinal  and  transverse  sections  should  be  made;  the  longitudinal  includ- 
ing at  least  two  of  the  cartilaginous  rings;  the  transverse  being  through  one  of  the 
rings. 

The   Bronchi. 

The  primary  bronchi  and  their  largest  branches  have  essentially 
the  same  structure  as  the  trachea  except  that  the  cartilaginous  rings 
are  not  as  complete. 

As  the  bronchi  decrease  in  calibre,  the  following  changes  take 
place  in  their  walls  (Figs.  152  and  153): 

(i)  The  epithelium  gradually  becomes  thinner.  In  a  bronchus 
of  medium  size  it  has  become  reduced  to  three  layers  of  cells,  which 
Kolliker  describes  as  an  outer  "basal"  layer,  a  middle  "replacing" 
layer,  and  a  surface  layer  of  ciliated  and  goblet  cells.  In  the  smaller 
bronchi  the  epithelium  is  reduced  to  a  single  layer  of  ciliated  cells. 


THE  RESPIRATORY  SYSTEM. 


243 


These  are  at  first  high,  but  become  gradually  lower  as  the  bronchi 
become  smaller,  until  in  the  terminal  branches  the  epithelium  is 
simple  cuboidal  and  non-ciliated. 


FIG.  152.— Transverse  Section  through  a  Large  and  a  Medium-size  Bronchus  of  the  Human 
Lung.  X  15.  (Technic  2,  p.  251.)  In  the  fibrous  coat  are  seen  the  bronchial  arteries  and 
veins,  a,  Epithelium;  l>,  stroma;  c,  muscularis  mucosa?;  d,  lung  tissue;  e,  fibrous  coat ; 
/,  plates  of  cartilage. 

(2)   The   stroma  decreases   in  thickness   as   the   bronchi    become 
smaller.      It   consists   of  loosely  arranged   white  and  elastic   fibres. 


•   /^    -  '        ■--■  \^- •■,•••• 


FIG.  153. — Transverse  Section  of  Small  Bronchus  from  Human  Lung.     X  115.     (Technic  2,  p. 
251.)     n,  Stroma  ;  />,  epithelium  ;  c,  muscularis  mucosas  ;  d,  fibrous  coat. 


There  is  considerable  diffuse  lymphatic  tissue,  and  in  some  places 
small  nodules  occur,  over  which  there  may  be  lymphoid  infiltration 
of  the  epithelium  (see  Tonsil,  page  141). 


244  THE   ORGANS. 

(3)  With  decrease  in  thickness  of  the  epithelium  and  of  the  stro- 
ma, the  thickness  of  the  mucosa  is  maintained  by  the  appearance  of 
a  layer  of  smooth  muscle.  In  the  larger  bronchi  this  is  a  continuous 
layer  of  circularly  disposed  smooth  muscle,  and  lies  just  external  to 
the  stroma,  forming  a  muscularis  mucosae.  As  the  bronchi  become 
smaller  the  muscularis  mucosas  becomes  thinner,  discontinuous,  and 
in  the  smallest  bronchi  is  represented  by  only  a  few  scattered  mus- 
cle cells. 

(4)  The  submucosa  decreases  in  thickness  with  decrease  in  the 
calibre  of  the  bronchi.  It  consists  of  loosely  arranged  connective 
tissue.  Mucous  glands  are  present  until  a  diameter  of  about  1  ram. 
is  reached,  when  they  disappear. 

I  5)  The  cartilages,  which  in  the  trachea  and  primary  bronchi  form 
nearly  complete  rings,  become  gradually  smaller,  and  finally  break 
up  into  short  disconnected  plates  (Fig.  152).  These  plates  decrease 
in  size  and  number,  and  are  absent  after  a  diameter  of  1  mm.  is 
reached. 

From  the  small  bronchi  are  given  off  terminal  bronchi.  These 
are  respiratory  in  character  and  are  described  with  the  lungs. 

The   Lungs. 

The  lung  is  built  upon  the  plan  of  a  compound  alveolar  gland, 
the  trachea  and  bronchial  ramifications  corresponding  to  duct  sys- 
tems, the  air  vesicles  to  gland  alveoli. 

The  surface  of  the  lung  is  covered  by  a  serous  membrane — the 
pulmonary  pleura — which  forms  its  capsule,  and  which  at  the  root  of 
the  lung,  or  hilum,  is  reflected  upon  the  inner  surface  of  the  chest 
wall  as  the  parietal  pleura.  From  the  capsule  broad  connective-tis- 
sue septa  pass  into  the  organ,  dividing  it  into  lobes.  From  the  cap- 
sule and  interlobar  septa  are  given  off  smaller  septa,  which  subdivide 
the  lobes  into  lobules. 

The  human  pulmonary  lobule  is  irregularly  pyramidal,  and  has  a 
diameter  of  from  1  to  3  cm.  The  amount  of  interlobular  connective 
tissue  is  so  small  that  no  distinct  separation  into  lobules  can  usually 
be  made  out.  The  pulmonary  lobule  constitutes  the  anatomic  unit 
of  lung  structure  in  the  same  sense  that  the  liver  lobule  constitutes 
the  anatomic  unit  of  that  organ.  The  most  superficial  lobules  are 
arranged  with  their  bases  against  the  pleura.  Flsewhere  in  the  lung 
the  lobules  have  an  irregular  arrangement. 


THE  RESPIRATORY  SYSTEM. 


245 


The  apex  of  each  lobule  is  the  point  of  entrance  of  a  small  bron- 
chus. This  gives  off  within  the  lobule  several  terminal  or  respi- 
ratory bronchi  {F'\g.    154,^;    Figs.  155   and    156,  BR).      From  each 


FIG.  154. — From  Lung  of  an  Ape.  The  bronchi  and  their  dependent  ducts  and  alveoli  have 
been  filled  with  quicksilver.  X  15.  (Kolliker,  after  Schulze.j  b,  Terminal  bronchus; 
a,  alveolar  duct ;    z",  alveoli. 

terminal  bronchus  open  from  three  to  six  narrow  passages — alveolar 
passages  or  alveolar  ducts  (Fig.  154,  a;  Figs.  155  and  156,  DA). 
The  alveolar  passages  open  into  wider  chambers — air  passages  or 
infnndibula.     The  latter  are  irregularly  pyramidal,  their  bases  being 


FIG.  155.— Camera  Lucida  Tracing  of  Calf's  Lung  (Miller).  Stippling  =  nuclei  of  epithelium 
and  position  of  smooth  muscle.  Pulmonary  artery  in  black.  B.R.,  Respiratory  bronchus  ; 
D.A.,  alveolar  duct ;  A.,  atrium  ;  A.S.,  air  sacs. 


directed  away  from  the  alveolar  passage.  From  the  sides  of  the 
alveolar  passage  and  from  the  infundibula  are  given  off  the  alveoli 
— air  vesicles  or  air  cells  (Fig.  154,  i;   Figs.  155  and  156,  AS). 

According  to  Miller  a  further  subdivision  of  the  alveolar  passage 


246 


THE   ORGANS. 


can  be  made.     He  describes  the  terminal  bronchus  as  about  0.5  mm. 
in  diameter,  and  as  opening  into  from  three  to  six  narrow  tubules, 


Fig.  156. — Camera  Lucida  Tracing  of  Section  of  Lung  of  Two  and  One-half  Months'  Old 
Child  (Miller).  Heavy  black  lines,  smooth  muscle;  pulmonary  artery  in  black;  B.R., 
respiratory    bronchus  ;  D.A.,  alveolar  duct  ;  A.,  atrium  ;  ^..S".,  air  sacs. 

the  vestibula.  Each  vestibulum  is  about  0.2  mm.  in  diameter,  and 
opens  into  several  larger,  nearly  spherical  chambers,  the  atria.  Each 
atrium  communicates  with  a  number  of  very  narrow — 0.14  mm. — air- 


FiG.  157.— From  Section  of  Cat's  Lung  Stained  with  Silver  Nitrate.  (Klein.)  (Technic  i, 
p.  m.i  Small  bronchus  surrounded  by  alveoli,  in  which  are  seen  both  flat  cells  (respira- 
tory epithelium),  and  cuboidal  cells  (foetal  cells). 

sac  passages  from  which  open  the  air  sacs.      From  the  latter  are  given 
off  on  all  sides,  the  air  cells  ox  alveoli.     Alveoli  are  not,  however, 


THE  RESPIRATORY  SYSTEM. 


247 


confined  to  the  periphery  of  the  air  sacs,  but  are  given  off  in  small 
numbers  from  the  terminal  bronchus,  and  in  constantly  increasing 
numbers  from  the  alveolar  ducts  and  infundibula. 

The  terminal  bronchus.  The  proximal  portion  of  the  terminal  or 
respiratory  bronchus  is  lined  by  a  simple  columnar  ciliated  epithe- 
lium, resting  upon  a  basement  membrane.  Beneath  this  is  a  richly 
elastic  stroma  containing  bundles  of  circularly  disposed  smooth  mus- 
cle cells.     The  epithelium  becomes  gradually  lower  and  non-ciliated, 


Fig.  158.— Section  Through  Three  Alveoli  of  Human  Lung.  X  235.  Weigert's  elastic-tissue 
stain  (technic  3,  p.  23)  to  show  arrangement  of  elastic  tissue,  a,  Alveolus  cut  through 
side  walls  only  ;  b,  alveolus  cut  through  side  walls  and  portion  of  bottom  or  top  ;  c,  alve- 
olus in  which  either  the  bottom  or  top  is  included  in  section. 


and  near  the  distal  end  of  the  terminal  bronchus  there  appear  small 
groups  or  islands  of  flat,  non-nucleated  epithelial  cells — respiratory 
epithelium. 

The  alveolar  passage.  Here  the  cuboidal  epithelium  is  almost 
completely  replaced  by  the  respiratory.  Beneath  the  epithelium  the 
walls  have  a  structure  similar  to  those  of  the  distal  end  of  the  termi- 
nal bronchus,  consisting  of  delicate  fibro-elastic  tissue  with  scattered 
smooth  muscle  cells.     The  basement  membrane  is  extremely  thin. 

The  air  passage.  The  epithelium  of  the  air  passage  consists  of 
two  kinds  of  cells,  respiratory  cells  and  so-called  "festal"  cells  (see 
Development,  page  251). 

The  respiratory  cells  (Fig.  157)  are  some  of  them  large,  flat,  non- 


248 


THE   ORGANS. 


nucleated  plates,  while  others  are  much  smaller,  non-nucleated  ele- 
ments. The  absence  of  nuclei  and  the  extremely  small  amount  of 
intercellular  substance  render  these  cells  quite  invisible  in  sections 
stained  by  the  more  common  methods.  The  cell  boundaries  are  best 
demonstrated  by  means  of  silver  nitrate  (technic  I,  p.  61). 


^- 


Fig.  T-g. — Parts  of  Four  Alveoli  from  Section  of  Injected  Human  Lung.  X  200.  (Technics, 
p.  251J  a,  Wall  of  alveolus  seen  on  flat;  c.  same,  but  only  small  part  of  alveolarwall  in 
plane  of  section  ;  b,  alveoli  in  which  plane  of  section  includes  only  side  walls  ;  alveolar 
wall  seen  on  edge. 

The  "foetal"  cells  are  granular,  nucleated  cells  which  are  scat- 
tered among  the  respiratory  cells.  In  the  embryonic  lung  the  air 
passages  and  alveoli  contain  only  this  type  of  cells. 

In  the  alveolar  passage  the  basement  membrane  almost  entirely 
disappears,  the  epithelium  being  supported  by  delicate  elastic  fibrils 
intermingled  with  a  few  white  fibrils  and  connective-tissue  cells. 

The  alveolus  is  similar  in  structure  to  the  alveolar  passage,  its 
walls  consisting  mainly  of  delicate  elastic  fibrils  supporting  respi- 
ratory and  foetal  cells.  Around  the  opening  of  the  alveolus  the  elas- 
tic fibres  are  more  numerous,  forming  a  more  or  less  definite  ring. 

The  interalvcolar  connective  tissue,  while  extremely  small  in 
amount,  serves  to  separate  the  alveoli  from  one  another.      Somewhat 


THE  RESPIRATORY  SYSTEM.  249 

thicker  connective  tissue  separates  the  alveoli  of  one  alveolar  passage 
from  those  of  another.  Still  stronger  connective-tissue  bands  sepa- 
rate adjacent  lobules. 

Blood-vessels. — Two  systems  of  vessels  distribute  blood  to  the 
lungs.  One,  the  broudiial  system,  carries  blood  for  the  nutrition  of 
the  lung  tissue.  The  other,  the  much  larger  pulmonary  system,  car- 
ries blood  for  the  respiratory  function. 

The  bronchia/  artery  and  the  pulmonary  artery  enter  the  lung  at 
its  hilum.  Within  the  lung  the  vessels  branch,  following  the  branch- 
ings of  the  bronchi,  which  they  accompany.  The  pulmonary  vessels 
are  much  the  larger  and  run  in  the  connective  tissue  outside  the 
bronchial  walls.  The  bronchial  vessels  lie  within  the  fibrous  coat  of 
the  bronchus.  A  section  of  a  bronchus  thus  usually  shows  the  large 
pulmonary  vessels,  one  on  either  side  of  the  bronchus,  and  two  or 
more  small  bronchial  vessels  in  the  walls  of  the  bronchus  (Fig.  152). 

The  pulmonary  lobule  forms  a  distinct  "  blood-vascular  unit."  A 
branch  of  the  pulmonary  artery  enters  the  apex  of  each  lobule  close 
to  the  lobular  bronchus,  and  almost  immediately  breaks  up  into 
branches,  one  of  which  passes  to  each  alveolar  passage.  From  these 
are  given  off  minute  terminal  arterioles  which  pass  to  the  central 
sides  of  the  alveolar  passages  and  alveoli,  where  they  give  rise  to  a 
rich  capillary  network.     This  capillary  network  is  extremely  close- 


Blood.  ""--  c 

Fig.  160. — Diagram   of  Tissues  Interposed  Between  Blood  and  Air  in  Alveolus,     a.  Respira- 
tory epithelium  ;  &,    basement  membrane  ;   c,  endothelium  of  capillary. 

meshed,  and  invests  the  alveoli  on  all  sides.  Similar  networks  in- 
vest the  walls  of  the  respiratory  bronchi,  the  alveolar  ducts  and  their 
alveoli.     All  of  these  capillary  networks  freely  anastomose. 

There  are  thus  interposed  between  the  blood  in  the  capillaries 
and  the  air  in  the  alveoli  only  three  extremely  thin  layers  :  (1)  The 
thin  endothelium  of  the  capillary  wall ;  (2)  the  single  layer  of  flat 
respiratory  epithelial  plates ;  and  (3)  the  delicate  basement  mem- 
brane upon  which  the  respiratory  epithelium  rests  (see  diagram,  Fig. 
160).  The  "foetal  "  cells  appear  to  lie  rather  between  the  capillaries 
than  upon  the  capillaries,  as  do  the  respiratory  cells. 

The  veins  begin  as  small  radicles,  one  from  the  base  of  each  alve- 
olus.    These  empty  into  small  veins  at  the  periphery  of  the  lobule. 


250  THE   ORGANS. 

These  veins  at  first  run  in  the  interlobular  connective  tissue  away 
from  the  artery  and  bronchus.  Later  they  empty  into  the  large  pul- 
monary trunks  which  accompany  the  bronchi. 

The  bronchial  arteries  break  up  into  capillary  networks  in  the 
walls  of  the  bronchi,  supplying  them  as  far  as  their  respiratory  divi- 
sions, beyond  which  point  the  capillaries  belong  to  the  pulmonary 
system.  The  bronchial  arteries  supply  the  walls  of  the  bronchi,  the 
bronchial  lymph  nodes,  the  walls  of  the  pulmonary  vessels,  and  the 
pulmonary  pleura.  Of  the  bronchial  capillaries  some  empty  into  the 
bronchial  veins,  others  into  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  of  the  lung  begin  as  small  lymph 
spaces  in  the  interalveolar  connective  tissue.  These  communicate 
with  larger  lymph  channels  in  the  interlobular  septa.  Some  of  these 
empty  into  the  deep  pulmonary  lymphatics,  which  follow  the  pulmo- 
nary vessels  to  the  lymph  glands  at  the  root  of  the  lung.  Others 
empty  into  the  superficial  pulmonary  lymphatics,  which  form  an 
extensive  subpleural  plexus  connected  with  small  subpleural  lymph 
nodes,  whence  by  means  of  several  larger  vessels  the  lymph  is  carried 
to  the  lymph  nodes  at  the  hilum. 

Nerves. — -Bundles  of  medullated  and  non-medullated  fibres  accom- 
pany the  bronchial  arteries  and  veins.  Small  sympathetic  ganglia 
are  distributed  along  these  nerves.  The  fibres  form  plexuses  in  the 
fibrous  layer  of  the  bronchi,  from  which  terminals  pass  to  the  muscle 
of  the  bronchi  and  of  the  vessel  walls  and  to  the  mucosa.  Free  end- 
ings upon  the  epithelium  of  bronchi,  air  passages,  and  alveoli  have 
been  described. 

Development  of  the  Respiratory  System. 

The  epithelium  of  the  respiratory  system  develops  from  ento- 
derm, the  connective-tissue  elements  from  mesoderm.  The  first  dif- 
ferentiation of  respiratory  system  appears  as  a  dipping  down  of  the 
entoderm  of  the  floor  of  the  primitive  pharynx.  The  tubule  thus 
formed  divides  into  a  larger  and  longer  right  branch,  which  sub- 
divides into  three  branches  corresponding  to  the  three  lobes  of  the 
future  right  lung,  and  a  smaller  and  shorter  left  branch,  which  sub- 
divides into  two  branches  corresponding  to  the  two  lobes  of  the 
future  left  lung.  By  repeated  subdivisions  of  these  tubules  the 
entire  bronchial  system  is  formed.  The  last  to  develop  are  the 
respiratory  divisions  of  the  bronchi  with  their  alveolar  passages  and 


THE  RES  P  IRA  TOR  Y  SYS  TEM.  2  5  1 

alveoli.  The  epithelium  of  the  air  passages  and  alveoli  is  at  first 
entirely  of  the  foetal-cell  type,  the  large  flat  respiratory  plates  appear- 
ing only  after  the  lungs  have  become  inflated.  The  fcetal  and  respi- 
ratory cells  of  the  adult  lung  have  therefore  the  same  embryonic 
origin.  During  the  early  stages  of  lung  development  the  mesoder- 
mic  tissue  predominates,  but  with  the  rapid  growth  of  the  tubules 
the  proportion  of  the  two  changes  until  in  the  adult  lung  the  meso- 
dermic  tissue  becomes  restricted  to  the  inconspicuous  pulmonary 
framework  and  the  blood-vessels. 

TECHNIC. 

(1)  The  technic  for  the  largest  bronchi  is  the  same  as  for  the  trachea  (technic 
3,  p.  242).     The  medium  size  and  small  bronchi  are  studied  in  sections  of  the  lung. 

(2)  Lung  and  Bronchi.  — Carefully  remove  the  lungs  and  trachea  (human,  dog, 
or  cat)  and  tie  into  the  trachea  a  cannula  to  which  a  funnel  is  attached.  Distend 
the  lungs  moderately  (pressure  of  two  to  four  inches)  by  pouring  in  formalin-Miil- 
ler's  fluid  (technic  5,  p.  5),  and  then  immerse  the  whole  in  the  same  fixative  for 
twenty-four  hours.  Cut  into  small  blocks,  using  a  very  sharp  razor  so  as  not  to 
squeeze  the  tissue,  harden  in  alcohol,  stain  thin  sections  with  hsematoxylin-eosin 
(technic  1,  p.  16),  and  mount  in  balsam  or  in  eosin-glycerin.  The  larger  bronchi 
are  found  in  sections  near  the  root  of  the  lung.  The  arrangement  of  the  pulmo- 
nary lobules  is  best  seen  in  sections  near  and  horizontal  to  the  surface.  Sections 
perpendicular  to  and  including  the  surface  show  the  pulmonary  pleura. 

(3)  Respiratory  Epithelium  (technic  1,  p.  61). 

(4)  Elastic  Tissue  of  the  Lung  (technic  3,  p.  23). 

(5)  Blood-vessels.—  For  the  study  of  the  blood-vessels,  especially  of  the  capil- 
lary networks  of  the  alveoli,  sections  of  injected  lung  should  be  made.  A  fresh 
lung  is  injected  (page  20)  with  blue  gelatin,  through  the  pulmonary  artery.  It  is 
then  hardened  in  alcohol,  embedded  in  celloidin,  and  thick  sections  are  stained 
with  eosin  and  mounted  in  balsam. 

The  Thyroid. 

The  thyroid  is  a  ductless  structure  built  upon  the  general  prin- 
ciple of  a  compound  alveolar  gland.  There  are  usually  two  lateral 
lobes  connected  by  a  narrow  band  of  glandular  tissue,  the  "isthmus.  " 
Each  lobe  is  surrounded  by  a  connective-tissue  capsule,  from  which 
septa  pass  into  the  lobe,  subdividing  it  into  lobules.  From  the  peri- 
lobular connective  tissue  finer  strands  extend  into  the  lobules,  sepa- 
rating the  alveoli.  The  latter  are  spherical,  oval,  or  irregular  in 
shape,  and  are  as  a  rule  non-communicating.  At  birth  most  of  the 
alveoli  are  empty,  but  soon  become  more  or  less  filled  with  a  peculiar 
substance  known  as  "colloid."  The  alveoli  are  lined  with  a  single 
layer  of  cuboidal  epithelial  cells.     Two  types  of  cells  are  recognized, 


252  THE  ORGANS. 

chief  cells  and  colloid  cells.  It  is  probable  that  these  represent  dif- 
ferent secretory  conditions  of  the  same  cell.  In  the  secretion  of 
colloid  the  chief  cell  seems  to  be  first  transformed  into  a  colloid 
cell.  The  latter  appears  in  some  cases  simply  to  pour  out  its  colloid 
secretion  into  the  lumen,  after  which  it  assumes  the  character  of  a 
chief  cell ;  in  other  cases  the  cell  appears  to  be  completely  trans- 
formed into  colloid,  its  place  being  taken  by  proliferation  of  the  chief 
cells.  In  certain  alveoli  which  are  much  distended  with  colloid  the 
lining  epithelium   is  flattened. 

The  blood  supply  of  the  thyroid  is  extremely  rich,  the  vessels 
branching  and  anastomosing  in  the  connective  tissue  and  forming 
dense  capillary  networks  around  the  alveoli. 

Lymphatics  accompany  the  blood-vessels  in  the  connective  tissue. 

Nerves  are  mainly  non-medullated  fibres  which  form  plexuses 
around  the  blood-vessels  and  in  the  connective  tissue  surrounding 
the  alveoli.  Terminals  to  the  secreting  cells  end  in  club-like  dilata- 
tions against  the  bases  or  between  the  epithelial  cells.  A  few  affer- 
ent medullated  fibres  are  found  in  the  plexuses  surrounding  the 
blood-vessels. 

Development. — The  median  portion  of  the  thyroid  or  isthmus 
originates  as  a  diverticulum  from  the  entoderm  of  the  primitive 
pharynx,  the  lateral  lobes  as  diverticula  from  the  fourth  visceral  cleft. 
These  three  bodies,  at  first  independent,  unite  to  form  the  thyroid 
and  become  entirely  separated  from  the  entoderm.  The  gland  at 
first  consists  of  solid  cords  of  cells.  Ingrowth  of  connective  tissue 
divides  these  into  groups  or  lobules,  and  at  the  same  time  breaks  up 
the  long  tubules  into  short  segments.  Dilatation  of  the  alveoli  oc- 
curs with  the  formation  of  colloid. 


The  Parathyroids. 

These  are  small  ductless  glands,  usually  four  in  number,  which 
lie  upon  the  lateral  lobes  of  the  thyroid.  They  consist  of  a  vascular 
connective  tissue  and  solid  anastomosing  cords  of  epithelial  cells. 
After  removal  of  the  thyroids  the  parathyroids  hypertrophy  and  ap- 
parently assume  the  function  of  the  thyroid. 


THE  RESPIRATORY  SYSTEM.  253 

TECHNIC. 

The  thyroid  and  parathyroid  glands  are  best  fixed  in  formalin-Midler's  fluid. 
Sections  may  be  stained  with  haematoxylin-eosin  or  hsmatoxylin-picro-acid-fuchsin 
and  mounted  in  balsam. 

General  References  for  Further  Study. 

Miller,  W.  S.  :  Das  Lungenlappchen,  seine  Blut-  und  Lymphgefasse. 
Councilman:   The   Lobule  of  the  Lung  and  Its  Relations  to  the  Lymphatics. 
Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 


CHAPTER    VIII. 


'% 


e 


THE    URINARY    SYSTEM. 

The    Kidney. 

The  kidney  is  a  compound  tubular  gland.      It  is  enclosed  by  a 
firm   connective-tissue   capsule,    the   inner   layer   of  which   contains 
smooth  muscle  cells.     In  many  of  the  lower  animals  and  in  the  human 
a  b  foetus    septa     extend    from    the 

capsule  into  the  gland,  dividing 
it  into  a  number  of  lobes  or 
renculi.  In  some  animals,  e.g., 
the  guinea-pig  and  rabbit,  the 
entire  kidney  consists  of  a  single 
renculus  (Fig.  161).  In  the  adult 
human  kidney  the  division  into 
renculi  is  not  complete,  the  per- 
ipheral parts  of  the  different  ren- 
culi blending.  Rarely  the  foetal 
division  into  renculi  persists  in 
adult  life,  such  a  kidney  being 
known  as  a  "  lobulated  kidney." 

On  the  mesially  directed  side 
of  the  kidney  is  a  depression 
known  as  the  hilum  (Fig.  161). 
This  serves  as  the  point  of  en- 
trance of  the  renal  artery  and  of 
exit  for  the  renal  vein  and  ureter. 
On  section  a  division  of  the 
organ  into  two  zones  is  apparent 
to  the  naked  eye  (Figs.  161  and 
162).  The  outer  zone  or  cortex  has  a  granular  appearance,  while  the 
inner  zone  or  medulla  shows  radial  striations.  This  difference  in 
appearance  between  cortex  and  medulla  is  mainly  due,  as  will  be 
seen    subsequently,    to    the    fact    that    in    the    cortex    the    kidney 

254 


% 


FIG.  161.  Longitudinal  Section  Through  Kid- 
ney of  Guinea-pig,  including  hilum  and 
beginning  of  ureter.  X  5.  (Technic  1, 
p.  269).  a,  Pelvis;  b,  papilla;  c,  wall  of 
pelvis;  d,  ureter;  e,  ducts  of  Bellini;/, 
cortical  pyamids ;  g;  medullary  rays;  //, 
cortex  ;  /,  medulla  ;  /,  renal  corpuscles. 


THE   URINARY  SYSTEM. 


255 


tubules  are  convoluted,  while  in  the  medulla  they  run  in  parallel 
radial  lines  alternating  with  straight  blood-vessels.  The  medullary 
portion  of  the   kidney  projects  into  the  pelvis,   or  upper    expanded 


i  Pelvis 

Fig.  162.  Fig.  163. 

FIG.  162.— Longitudinal  Section  of  Kidney  Through  Hilum.  a,  Cortical  pyramid;  b,  medul- 
lary ray  ;  c,  medulla  ;  d,  cortex  ;  e,  renal  calyx  ;  f,  hilum  ;  g,  ureter  ;  h,  renal  artery  ; 
i,  obliquely  cut  tubules  of  medulla  ;  /and  k,  renal  arches  ;  /,  column  of  Bertini  ;  in,  con- 
nective tissue  and  fat  surrounding  renal  vessels  ;  //,  medulla  cut  obliquely  ;  0,  papilla  ; 
f,  medullary  pyramid.     (Merkel-Henle.) 

FIG.  163.— Scheme  of  Uriniferous  Tubule  and  of  the  Blood-vessels  of  the  Kidney  showing 
their  relation  to  each  other  and  to  the  different  parts  of  the  kidney.  G,  Glomerulus  ; 
BC,  Bowman's  capsule;  A*  neck;  PC,  proximal  convoluted  tubule;  6',  spiral  tubule; 
D,  descending  arm  of  Henle's  loop;  L,  Henle's  loop  ;  A,  ascending  arm  of  Henle'sloop; 
/,  DC,  distal  convoluted  tubule  ;  AC,  arched  tubule  ;  SC,  straight  collecting  tubule  ;  ED, 
duct  of  Bellini  ;  A,  arcuate  artery,  and  V,  arcuate  vein,  giving  off  interlobular  vessels 
to  cortex  and  vasa  recta  to  medulla  ;  a,  afferent  vessel  of  glomerulus  ;  e,  efferent  vessel 
of  glomerulus;  c,  capillary  network  in  cortical  labyrinth;  s,  stellate  veins;  vr,  vasa 
recta  and  capillary  network  of  medulla. 

beginning  of  the  ureter  (Figs.  161  and  162)  in  the  form  of  papilla. 
The  number  of  papillae  varies  from  ten  to  fifteen,  corresponding  to 
the  number   of  lobules   in  the   foetal  kidney.      The  pyramidal   seg- 


256 


THE   ORGANS. 


ment  of  medulla,  the  apex  of  which  is  a  papilla — in  other  words, 
the  medullary  portion  of  a  foetal  lobe — is  known  as  a  medullary 
or  Malpighian  pyramid.  The  extensions  downward  of  cortical 
substance  between  the  Malpighian  pyramids  constitute  the  columns 
of  Bertini  or  septa  raiis.  Radiating  lines — medullary  rays  or 
pyramids  of  Ferrein — extend  outward  from  the  base  of  each  Mal- 
pighian pyramid  into  the  cortex  (Fig.  162).  As  the  rays  extend  out- 
ward in  groups  they  outline  pyramidal  cortical  areas.  These  are 
known  as  the  cortical  pyramids  or  cortical  labyrinths. 

The  secreting  portion  of  the  kidney  is  composed  of  a  large  num- 
ber of  long  tortuous  tubules,  the  uriniferous  tubules. 

Each  uriniferous  tubule  begins  in  an  expansion  known  as 
Bowman  s  capsule  (Figs.  163,  B  C,  and  164).     This  encloses  a  tuft 


FIG.  164. — Diagrams  Illustrating  Successive  Stages  in  Development  of  the  Renal  Corpuscle. 
1  and  2,  Approach  of  blood-vessel  and  blind  end  of  tubule  ;  3,  invagination  of  tubule  by 
blood-vessels  ;  4  and  5,  later  stages,  showing  development  of  glomerulus  and  of  the  two- 
layered  capsule  of  the  renal  corpuscle,  the  outer  layer  being  the  capsule  of  Bowman  con- 
tinuous with  the  epithelium  of  the  first  convoluted  tubule. 


of  blood  capillaries,  the  glomerulus.  Bowman's  capsule  and  the 
glomerulus  together  constitute  the  Malpighian  body  or  renal  cor- 
puscle. As  it  leaves  the  Malpighian  body  the  uriniferous  body 
becomes  constricted  to  form  the  neck  (Figs.  163,  N,  and  164).  It 
next  broadens  out  into  a  greatly  convoluted  portion,  the  first  ox  proxi- 
mal convoluted  tubule.  The  Malpighian  body,  the  neck,  and  the  first 
convoluted  tubule  are  situated  in  the  cortical  pyramid  (Fig.  163). 
The  tubule  next  takes  a  quite  straight  course  downward  into  the 
medulla — descending  arm  of  Henle's  loop  (Fig.  163,  D) — turns 
sharply  upon  itself — /fculc's  loop  (Fig.  163,  L) — and  passes  again 
toward  the  surface — ascending  arm  op  Henle's  loop  (Fig.  163)  A, — 


THE   URINARY  SYSTEM.  257 

through  the  medulla  and  medullary  ray.  Leaving  the  medullary  ray, 
it  enters  a  cortical  pyramid  (probably  as  a  rule  the  same  pyramid 
from  which   it  took  origin)  to  become  the  second  or  distal  convoluted 


.«?.«.   V    ;,.*    V  m  *  «."    ■   E    "      ^  ' 


V" 


FIG.   165. — Malpighian  Body  from  Human  Kidney.     X  280.     (Technic  2,  p.  269).     a,  Bowman's 
capsule  ;  l>,  neck  ;  c,  first  convoluted  tubule  ;  d,  afferent  and  efferent  vessels. 

tubule  (Fig.  163,  DC).  This  passes  into  the  arched  tubule  {AC) 
which  enters  a  medullary  ray  and  continues  straight  down  through 
the  medullary  ray  and  medulla  as  the  straight  or  collecting  tubule 
(SC).      During   its    course    the   collecting    tubule    receives     other 


"-•"■•■    ■;.,:>  .  p.  v.r;      ^r\-j:^  ^     J 

A 

Fig.  166.— Proximal  Convoluted   Tubules  of  Human  Kidney.     X  350.     (Technic  2,   p.  269.)    A, 

Cross-section  ;  B,  oblique  section. 

arched    tubules.     As    it    descends    it    becomes    broader,  enters    the 
papilla,  where  it  is  known  as  the  duct  of  Bellini  {ED),  and  opens 
on  the  surface  of  the  papilla  into  the  kidney  pelvis.     About  twenty 
17 


THE   ORGANS. 


ducts  of  Bellini  open  upon  the  surface  of  each  papilla,  their  open- 
ings being  known  as  the  foramina  papillaria. 

Each  tubule  consists  of  a  delicate  homogeneous  membra  ua  propria 
upon  which  rests  a  single  layer  of  epithelial  cells.  The  shape  and 
structure  of  the  epithelium  differ  in  different  portions  of  the  tubule. 

r.  The  Malpighian  body  is  spheroidal,  and  has  a  diameter  of  from 
1 20  to  200  a.  The  structure  of  the  Malpighian  body  can  be  best 
understood  by  reference  to  its  development  (Fig.  164).  During  the 
development  of  the  uriniferous  tubules  and  of  the  blood-vessels  of  the 


1       Z 


fl 


• 


ft 


m 


m 


FIG.  167.— Tubules  of  Human  Kidney.  X  560.  From  longitudinal  section.  (Technic  2,  p.  269.) 
1,  Descending  arm  of  Henle's  loop  ;  2,  ascending  arm  of  Henle's  loop  ;  3,  collecting  tubule  ; 
4,  duct  of  Bellini.  Beneath  the  longitudinal  sections  are  seen  cross  sections  of  the  same 
tubules. 

kidney  the  growing  end  of  a  vessel  meets  the  growing  end  of  a  tubule 
in  such  a  way  that  there  is  an  invagination  of  the  tubule  by  the 
blood-vessel  (see  Fig.  164).  The  result  is  that  the  end  of  the  ves- 
sel which  develops  a  tuft-like  network  of  capillaries — the  glomerulus 
—  comes  to  lie  within  the  expanded  end  of  the  tubule,  which  thus 
forms  a  two-layered  capsule  for  the  glomerulus.  One  layer  of  the 
capsule  closely  invests  the  tuft  of  capillaries.  This  by  modification 
of  the  original  tubular  epithelium  is  finally  composed  of  a  single  layer 
of  flat  epithelial  cells  with  projecting  nuclei.     The  outer  layer  of  the 


THE    URINARY  SYSTEM.  259 

capsule  lies  against  the  delicate  connective  tissue  which  surrounds 
the  Malpighian  body.  This  layer  consists  of  a  similar  though  slight- 
ly higher  epithelium  and  is  known  as  Bowman  s  capsule.  Between 
the  glomerular  layer  of  the  capsule  and  Bowman's  capsule  proper  is  a 
space  which  represents  the  beginning  of  the  lumen  of  the  uriniferous 
tubule  (Fig.  165),  the  epithelium  of  Bowman's  capsule  being  directly 
continuous  with  that  of  the  neck  of  the  tubule. 

2.  The  Neck. — This  is  short  and  narrow,  and  is  lined  by  a  few 
cuboidal  epithelial  cells.  Toward  its  glomerular  end  the  epithelium 
is  transitional  between  the  flat  epithelium  of  Bowman's  capsule  and 
the  cuboidal  epithelium  of  the  neck  proper.  At  its  other  end  the 
epithelium  of  the  neck  becomes  larger  and  more  irregular  as  it  passes 
over  into  that  lining  the  next  division  of  the  tubule. 

3.  The  first  or  proximal  convoluted  tubule  (Fig.  166)  measures 
from  40  to  70  fj.  in  diameter.  It  is  lined  by  irregularly  cuboidal  or 
pyramidal  epithelium,  with  very  indistinct  demarcation  between  the 
cells.  The  cytoplasm  is  granular,  and  the  granules  are  arranged  in 
rows,  giving  the  cell  a  striated  appearance.  This  is  especially 
marked  at  the  basal  end  of  the  cell  where  the  nucleus  is  situated. 
A  zone  of  fine  striations  along  the  free  surface  frequently  presents 
somewhat  the  appearance  of  cilia. 

4.  The  descending  arm  of  Henle 's  loop  is  narrow  (Fig.  167,  /),  10 
to  15//  in  diameter.  It  is  lined  by  a  simple  flat  epithelium.  The 
part  of  the  cell  which  contains  the  nucleus  bulges  into  the  lumen, 
and  as  the  nuclei  of  opposite  sides  of  the  tubule  usually  alternate, 
longitudinal  sections  are  apt  to  present  a  wavy  appearance. 

5.  Henle ' s  Loop. — The  epithelium  here  changes  from  the  flat  of 
the  descending  arm  to  the  cuboidal  of  the  ascending  arm.  The  exact 
point  where  the  transition  occurs  varies.  It  may  take  place  during 
the  turn  of  the  loop,  or  in  either  the  ascending  or  descending  arm. 

6.  The  ascending  arm  of  Henle' s  loop  (Fig.  167,  2)  is  broader 
than  the  descending,  measuring  from  20  to  30,7.  in  diameter.  Its 
epithelium  is  cuboidal  with  granular  striated  protoplasm.  The  cells 
thus  resemble  those  of  the  convoluted  tubule,  but  are  smaller,  more 
regular,  and  less  granular. 

7.  The  second  or  distal  convoluted  tubule  has  a  diameter  of  40  to 
50  //.  It  is  much  less  tortuous  than  the  first  convoluted  tubule.  Its 
epithelium  is  similar  to  that  lining  the  first  convoluted  tubule  except 
that  it  is  slightly  lower  and  less  distinctly  striated. 


260  THE   ORGANS. 

8.  The  arched  tubule  has  a  somewhat  wider  lumen  than  the  second 
convoluted.  It  is  lined  with  a  low  cuboidal  epithelium  with  only 
slightly  granular  cytoplasm. 

9.  The  straight  or  collecting  tubule  (Fig.  167,  J)  has  at  its  com- 
mencement at  the  apex  of  a  medullary  ray  a  diameter  about  the  same 
as  that  of  the  arched  tubule.      As  it  descends  it  receives  other  arched 


MR 


Fig.  168.— Cross  Section  Through  Cortex  of  Human  Kidney.  X  60.  (Technic2,  p.  269.)  a.  Con- 
voluted tubules  of  cortical  pyramid  ;  d,  interlobular  artery  ;  c,  medullary  rays  ;  d,  Mal- 
pighian  bodies. 

tubules,  and  increases  in  diameter  until  in  the  ducts  of  Bellini  (Fig. 
167,  </)  of  the  papilla  it  has  a  diameter  of  from  200  to  300,".  and  a 
widely  open  lumen.  The  epithelium  is  at  first  low  and  gradually 
increases  in  height.  In  the  ducts  of  Bellini  it  is  of  the  high  colum- 
nar type.  The  cytoplasm  of  these  cells  contains  comparatively  few 
granules,  thus  appearing  transparent  in  contrast  with  the  granular 
cytoplasm  of  the  ascending  arms  or  Ilenle's  loops  and  of  the  con- 
voluted tubules. 

The  epithelium  of  the  uriniferous  tubule  rests  upon  an  apparently 
structureless  basement  membrane.  Ruhle  describes  the  basement 
membrane  as  consisting  of  delicate  longitudinal  and  circular  connec- 
tive-tissue fibrils.  He  regards  the  fibrils  as  merely  a  more  regular 
arrangement    of    the    interstitial    connective    tissue.     According   to 


THE   URINARY    SYSTEM.  261 

Riihle  the  epithelium  simply  rests  upon  the  basement  membrane, 
being  in  no  way  connected  with  it. 

Of  the  function  of  the  different  parts  of  the  uriniferous  tubule 
our  knowledge  is  extremely  limited.  The  experiments  of  Heiden- 
hain  tend  to  prove  that  the  urinary  solids  are  secreted  mainly  or 
wholly  by  the  cells  of  the  proximal  convoluted  tubule  and  of  the  as- 
cending arm  of  Henle's  loop,  the  other  parts  of  the  tubule  allowing 
only  water  to  pass  through  their  epithelium. 

Blood-vessels  (diagram,  Fig.  170). — The  blood  supply  to  the  kid- 
ney is  rich  and  the  blood-vessels  come  into  intimate  relations  with 
the  tubules. 

The  renal  artery  enters  the  kidney  at  the  hilum,  and  immediately 
splits   up   into  a  number  of  branches — the  interlobar  arteries   (Fig. 


■W     ^    /A  ^1       C*V 


§        ®>r\    ,G 


'''II 


^  v  ft      JS^^S 


/> 

FIG.  169.— Cross  Section  Through  Medulla  of  Human  Kidney,  X  465.  (Technic  2,  p.  169.)  <?, 
Capillaries  ;  />,  collecting  tubule  ;  c,  asce'nding  arms  of  Henle's  loops  ;  if,  descending 
arms  of  Henle's  loops. 

170).  These  give  off  small  twigs  to  the  calyces  and  capsule,  and 
then  without  further  branching  pass  between  the  papillae  through  the 
medulla  to  the  junction  of  medulla  and  cortex.  Here  they  bend 
sharply  at  right   angles  and  following  the    boundary   line  between 


262 


THE   ORGANS. 


cortex  and  medulla,  form  a  series  of  arches,  the  arterice  arciformes 
or  arcuate  arteries.  From  the  arcuate  arteries  two  sets  of  vessels 
arise,  one  supplying  the  cortex,  the  other  the  medulla  (Figs.  163 
and  170). 

The  arteries  to  the  cortex  spring  from  the  outer  convex  sides  of 
the  arterial  arches,  and  as  the   interlobular  arteries  pursue  a   quite 

A  B 

c 

D 


PIG.  170  —  Diagram  to  Illustrate  (left)  the  Course  of  the  Uriniferous  Tubule  ;  (right)  the  Course 
of  the  Renal  Vessels.  (Szymonowicz.)  A,  B,  C\  I)  form  the  kidney  lobules ;  a,  afferent 
vessel  ;  ,,  efferent  vessel  of  glomerulus  ;  i,  Bowman's  capsule  ;  2,  first  convoluted  tubule  ; 
3,  descending  arm  of  Henle'sloop;  4,  ascending  arm  of  Henle's  loop;  5,  second  convoluted 
tubule;  6  and  7,  collecting  tubules;  3,  duct  of  Bellini;  /',  interlobular  artery;  c,  inter- 
lobular vein  ;  d,  renal  arch  (arcuate  artery  above  and  arcuate  vein  below)  ;  /",  interlobar 
vein  ;  .<',  interlobar  artery  ;  //,  medulla  ;  /,  medullary  ray  ;  /,  cortex. 


straight  course  through  the  cortical  pyramids  toward  the  surface, 
about  midway  between  adjacent  medullary  rays.  From  each  inter- 
lobular artery  arc  given  off  numerous  short  lateral  branches,  each  one 


THE   URINARY  SYSTEM.  263 

of  which  passes  to  a  Malpighian  body.  Entering  a  Malpighian  body 
as  its  afferent  vessel,  the  artery  breaks  up  into  a  number  of  small 
arterioles,  which  in  turn  give  rise  to  the  groups  of  capillaries  which 
form  the  glomerulus.  Each  group  of  glomerular  capillaries  arising 
from  a  single  arteriole  is  separated  from  its  neighbors  by  a  rather 
larger  amount  of  connective  tissue  than  that  which  separates  the 
individual  capillaries.  This  gives  to  the  glomerulus  its  lobular  ap- 
pearance. From  the  smaller  glomerular  capillaries  the  blood  passes 
into  somewhat  larger  capillaries,  which  unite  to  form  the  efferent 
vessel  of  the  glomerulus.  As  afferent  and  efferent  vessels  lie  side 
by  side,  the  glomerulus  has  the  appearance  of  being  suspended  from 
this  point.  The  entire  vascular  system  of  the  glomerulus  is 
arterial. 

After  leaving  the  glomerulus,  the  efferent  vessel  breaks  up  into  a 
second  system  of  capillaries,  which  form  a  dense  network  among  the 
tubules  of  the  cortical  pyramids  and  of  the  medullary  rays.  The 
mesh  corresponds  to  the  shape  of  the  tubules,  being  irregular  in  the 
pyramids,  long  and  narrow  in  the  rays.  In  these  capillaries  the 
blood  gradually  becomes  venous  and  passes  into  the  interlobular  veins. 
These  accompany  the  interlobular  arteries  to  the  boundary  between 
cortex  and  medulla,  where  they  enter  the  arcuate  veins,  which  accom- 
pany the  arcuate  arteries  (Fig.  170). 

In  addition  to  the  distribution  just  described,  some  of  the  inter- 
lobular arteries  extend  to  the  surface  of  the  kidney,  where  they  enter 
the  capsule  and  form  a  network  of  capillaries  which  anastomose  with 
capillaries  of  the  suprarenal,  recurrent,  and  phrenic  arteries.  A 
further  collateral  circulation  is  established  by  branches  of  the  above- 
named  arteries  penetrating  the  kidney  and  forming  capillary  networks 
within  the  cortex,  even  supplying  some  of  the  more  superficial 
glomeruli.  The  most  superficial  of  the  small  veins  which  enter  the 
interlobular  are  arranged  in  radial  groups,  having  the  interlobular 
veins  as  their  centres.  These  lie  just  beneath  the  capsule,  and  are 
known  as  the  stellate  veins  of  Verheyn.  In  addition  to  capillary 
anastomoses,  direct  communication  between  arteries  and  veins  of 
both  cortex  and  medulla,  by  means  of  trunks  of  considerable  size,  has 
been  described. 

The  lymph  vessels  of  the  kidney  are  arranged  in  two  systems,  a 
superficial  system  which  ramifies  in  the  capsule,  and  a  deep  system 
which   accompanies   the  arteries  to  the  parenchyma   of  the   organ. 


264  THE   ORGANS. 

Little  is  known  of  the  relation   of   the   lymphatics  to  the  kidney 
tubules. 

Nerves. — These  are  derived  from  both  cerebro-spinal  and  sym- 
pathetic systems.  The  medullated  fibres  appear  to  pass  mainly  to 
the  walls  of  the  blood-vessels  which  supply  the  kidney  capsule. 
Plexuses  of  fine  non-medullated  fibres  (sympathetic)  accompany  the 
arteries  to  the  glomeruli.  Delicate  terminals  have  been  described  as 
passing  from  these  plexuses,  piercing  the  basement  membrane  and 
ending  freely  between  the  epithelial  cells  of  the  tubules. 

The   Kidney-Pelvis   and   Ureter. 

The  kidney-pelvis,  with  its  subdivisions  the  calyces,  and  the  ureter 
constitute  the  main  excretory  duct  of  the  kidney.  Their  walls  con- 
sist of  three  coats  :  an  inner  mucous,  a  middle  muscular,  and  an  outer 
fibrous. 

The  mucosa  is  lined  by  epithelium  of  the  transitional  type. 
There  are  from  four  to  eight  layers  of  cells,  the  cell  outlines  are 
usually  well  defined,  and  the  surface  cells  instead  of  being  dis- 
tinctly squamous  are  only  slightly  flattened.  Less  commonly  large 
flat  plate-like  cells,  each  containing  several  nuclei,  are  present. 
The  cells  rest  upon  a  basement  membrane,  beneath  which  is  a  stroma 
of  delicate  fibro-elastic  tissue  rich  in  cells.  Diffuse  lymphatic  tis- 
sue frequently  occurs  in  the  stroma,  especially  of  the  pelvis.  Occa- 
sionally the  lymphatic  tissue  takes  the  form  of  small  nodules. 
Mucous  glands  in  small  numbers  are  found  in  the  stroma  of  the  pelvis 
and  upper  part  of  the  ureter.  There  is  no  distinct  submucosa, 
although  the  outer  part  of  the  stroma  is  sometimes  referred  to  as 
such. 

The  muscularis  consists  of  an  inner  longitudinal  and  an  outer 
circular  layer.  In  the  lower  part  of  the  ureter  a  discontinuous  outer 
longitudinal  layer  is  added. 

The  fibrosa  consists  of  loosely  arranged  connective  tissue  and 
contains  many  large  blood- vessels.  It  is  not  sharply  limited  exter- 
nally, but  blends  with  the  connective  tissue  of  surrounding  structures, 
and  serves  to  attach  the  ureter  to  the  latter. 

The  larger  blood-vessels  run  in  the  fibrous  coat.  From  these, 
branches  pierce  the  muscular  layer,  give  rise  to  a  capillary  network 
among  the  muscle  cells,  and  then  pass  to  the  mucosa,  in  the  stroma 


THE   URINARY  SYSTEM.  265 

of  which  they  break  up  into  a  rich  network  of  capillaries.  The  veins 
follow  the  arteries. 

The  lymphatics  follow  the  blood-vessels,  being  especially  numer- 
ous in  the  stroma  of  the  mucosa. 

Nerves. — Plexuses  of  both  medullated  and  non-medullated  fibres 
occur  in  the  walls  of  the  ureter  and  pelvis.  The  non-medullated 
fibres  pass  mainly  to  the  cells  of  the  muscularis.  Medullated  fibres 
enter  the  mucosa  where  they  lose  their  medullary  sheaths.  Termi- 
nals of  these  fibres  have  been  traced  to  the  lining  epithelium. 

The   Urinary   Bladder. 

The  walls  of  the  bladder  are  similar  in  structure  to  those  of  the 
ureter. 

The  mucous  membrane  is  thrown  up  into  folds  or  is  comparatively 
smooth,  according  to  the  degree  of  distention  of  the  organ.  The 
epithelium  is  of  the  same  general  type — transitional  epithelium  (see 
page  57) — as  that  of  the  ureter.  The  number  of  layers  of  cells  and 
the  shapes  of  the  cells  depend  largely  upon  whether  the  bladder  is 
full  or  empty.  In  the  collapsed  organ  the  superficial  cells  are  cu- 
boidal  or  even  columnar,  their  under  surfaces  being  marked  by  pit- 
like depressions  caused  by  pressure  of  underlying  cells.  Beneath 
the  superficial  cells  are  several  layers  of  polygonal  cells,  while  upon 
the  basement  membrane  is  the  usual  single  layer  of  small  cuboidal 
cells.  In  the  moderately  distended  bladder  the  superficial  cells 
become  flatter  and  the  entire  epithelium  thinner  (Fig.  171).  In  the 
distended  organ  there  is  still  further  flattening  of  the  superficial  cells 
and  thinning  of  the  entire  epithelium.  The  stroma  consists  of  fine 
loosely  arranged  connective  tissue  containing  many  lymphoid  cells 
and  sometimes  small  lymph  nodules.  It  merges  without  distinct 
demarcation  into  the  less  cellular  submucosa  (Fig.  171,  c). 

The  three  muscular  layers  of  the  lower  part  of  the  ureter  are  con- 
tinued on  to  the  bladder,  where  the  muscle  bundles  of  the  different 
layers  interlace  and  anastomose,  but  can  be  still  indistinctly  differ- 
entiated into  an  inner  longitudinal,  a  middle  circular,  and  an  outer 
longitudinal  layer  (Fig.   171,  d,  c,f). 

The  fibrous  layer  is  similar  to  that  of  the  ureter,  and  attaches  the 
organ  to  the  surrounding  structures. 

The  blood-  and  lymph-vessels  have  a  distribution  similar  to  those 
of  the  ureter. 


266  THE   ORGANS. 

Nerves. — Sensory  medullated  fibres  pierce  the  muscularis,  branch 
repeatedly  in  the  stroma,  lose  their  medullary  sheaths,  and  terminate 
among  the  cells  of  the  lining  epithelium.      Sympathetic  fibres  form 

•-  ■"'       ■  „i:^  ■'-'-■■ ;''  i&&d£*     .•'i*...-j~fxf.   ~"'~"~^r~.  —  —  |  ,. 


.--V 


Fir,.  171.— Vertical  Section  through  Wall  of  moderately  distended  Human  Bladder.  X  60. 
(Technic  5,  p.  269.)  1/,  Epithelium,  b,  stroma,  of  mucous  membrane;  c,  submucosa;  d, 
inner  muscle  layer  ;  e,  middle  muscle  layer  ;  /,  outer  muscle  layer. 

plexuses  in  the  fibrous  coat,  where  they  are  interspersed  with  numer- 
ous  small   groups  of  ganglion  cells.      Axones   of  these   sympathetic 
neurones  penetrate  the  muscularis.     Here  they  form  plexuses,  from 
which  are  given  off  terminals  to  the  individual  muscle  cells. 
For  development  of  urinary  system  see  page  308. 

The  Adrenal. 

The  adrenal  is  a  ductless  gland  situated  on  the  upper  and  ante- 
rior surface  of  the  kidney.  It  is  surrounded  by  a  capsule  and  con- 
sists of  an  outer  /.one  or  cortex  and  a  central  portion  or  medulla. 

The  CAPSULE  (Fig.  172,  A)  is  composed  of  fibrous  connective 
tissue  and  smooth  muscle.  In  the  outer  part  of  the  capsule  the  con- 
nective tissue  is  loosely  arranged  and  merges  with  the  surrounding 
fatty  areolar  tissue.      The  inner   layer  of  the  capsule  is  more  dense 


THE   URINARY  SYSTEM. 


267 


SPs    1 


* 


1-5 


and  forms  a  firm   investment  for  the  underlying  glandular  tissue. 
From  the  capsule  trabecular  extend  into  the  organ  forming  its  frame- 
work and  outlining  compartments,  which  contain  the  glandular  epi- 
thelium.     This   connective  tissue  is 
reticular  in  character. 

The  cortex  (Fig.  172.  B)  is  sub- 
divided into  three  layers  or  zones  : 
(a)  A  narrow,  superficial  layer,  the 
glomern  lar  zone  ;  (b)  a  broad  middle 
layer,  the  fascicular  zone  ;  and  (r)  a 
narrow  deep  layer,  the  reticular  zone. 
The  names  of  the  layers  are  indica- 
tive of  the  shape  of  the  connective- 
tissue-enclosed  compartments  and  of 
the  contained  groups  of  gland  cells. 
In  the  glomerular  zone  (Fig.  172, 
a)  the  high,  irregularly  columnar  epi- 
thelium is  arranged  in  spherical  or 
oval  groups.  The  protoplasm  of  the 
cells  is  granular,  and  their  nuclei  are 
rich  in  chromatin.  In  the  fascicular 
zone  (Fig.  172,  b)  polyhedral  cells  are 
arranged  in  long  columns  or  fascicles. 
The  cytoplasm  is  granular  and  usu- 
ally contains  some  fat  droplets.  The 
nuclei  are  poor  in  chromatin.  In  the 
reticular  zone  (Fig.  172,  c)  similar 
though  somewhat  more  darkly  stain- 
ing cells  form  a  coarse  reticulum  of 
irregular  anastomosing  cords. 

The  medulla  (Fig.  172,  C)  con- 
sists Of  Spherical  and  Oval  groups  and    Fig.   lya.-Vertical    Section    of    Adrenal. 

COrds  Of  polygonal  Cells.       After  ako-        ^kel-Iienle.)  .4,  Capsule  ;  B,  cortex-, 
1       J  °  C,  medulla  ;  a,  glomerular  zone  ;  b,  fas- 

hol   or   formalin  fixation  these    cells 

take  a  paler  stain  than  those  of  the 

cortex.     After  fixation  in  solutions  containing  chromic  acid  or  chrome 

salts  the  cells  of  the  medulla  assume  a  peculiar  deep  brown  color, 

which  cannot  be  removed    by  washing   in  water  and  which  is  quite 

characteristic  of  these  ceils. 


YC 


cicular  zone  ;  c,  reticular  zone  ;  v,  vein 
in  medulla. 


268  THE   ORGANS. 

Blood-vessels — The  arteries  supplying  the  adrenal  first  form  a 
poorly  defined  plexus  in  the  capsule.  From  this  are  given  off  three 
sets  of  vessels — one  to  the  capsule,  one  to  the  cortex,  and  one  to  the 
medulla.  The  first  set  breaks  up  into  a  network  of  capillaries,  which 
supply  the  capsule.  The  vessels  to  the  cortex  break  up  into  capil- 
lary networks,  the  shape  of  the  mesh  corresponding  to  the  arrange- 
ment of  the  connective  tissue  in  the  different  zones.  The  vessels 
to  the  medulla  pass  directly  through  the  cortex  without  branching 
and  form  dense  capillary  networks  among  the  groups  of  medullary 
cells.  The  relations  of  the  capillaries  to  these  gland  cells  are  ex- 
tremely intimate,  especially  in  the  reticular  zone  and  medulla,  where 
the  cells  in  many  cases  immediately  surround  the  capillaries  in  much 
the  same  manner  as  the  glandular  cells  of  a  tubular  gland  surround 
their  lumina.  From  the  capillaries  of  both  cortex  and  medulla  small 
veins  arise.  These  unite  to  form  larger  veins  which  empty  into  one 
or  two  main  veins  situated  in  the  centre  of  the  medulla. 

Lymphatics — These  follow  in  general  the  course  of  the  blood- 
vessels. The  exact  distribution  of  the  adrenal  lymph  system  has  not 
been  as  yet  satisfactorily  determined. 

Nerves. — The  nerve  supply  of  the  adrenal  is  so  rich  and  the  nerve 
elements  of  the  gland  are  so  abundant  as  to  have  led  to  its  classification 
by  some  among  the  organs  of  the  nervous  system.  Both  medullated 
and  non-medullated  fibres- — but  chiefly  the  latter — form  plexuses  in 
the  capsule,  where  they  are  associated  with  groups  of  sympathetic 
ganglion  cells.  From  the  capsular  plexuses  fine  fibres  pass  into  the 
cortex,  where  they  form  networks  around  the  groups  of  cortical  cells. 
The  nerve  terminals  of  the  cortex  apparently  do  not  penetrate  the 
groups  of  cells.  Bundles  of  nerve  fibres,  larger  and  more  numerous 
than  those  to  the  cortex,  pass  through  the  cortex  to  the  medulla. 
Here  they  form  unusually  dense  plexuses  of  fibres,  which  not  only 
surround  the  groups  of  cells,  but  penetrate  the  groups  and  surround 
the  individual  cells.  Associated  with  the  plexuses  of  the  medulla, 
less  commonly  of  the  cortex,  are  numerous  conspicuous  groups  of 
sympathetic  ganglion  cells. 

Development. — The  cortex  of  the  adrenal  develops  from  meso- 
blast.  As  to  the  origin  of  the  medulla  two  views  are  held.  Accord- 
ing to  one,  the  medullary  cells  are  also  derived  from  mesoderm  and 
represent  a  further  differentiation  of  the  cortical  cells.  According 
to  others,    the    medulla   has   an   entirely  independent   origin,    being 


THE   URINARY  SYSTEM.  269 

derived  from  ectoderm,  as  part  of  the  peripheral  sympathetic  nervous 
system.  Flint  describes  the  adrenal  of  a  3.5  cm. -long  pig  embryo 
as  consisting  wholly  of  cortical  substance,  surrounded  by  a  capsule, 
which  is  closely  associated  with  a  plexus  of  the  sympathetic.  Cells 
of  the  type  of  medullary  cells  first  appear  just  beneath  the  capsule, 
whence  they  later  migrate  to  the  centre  of  the  organ.  This  migra- 
tion accounts  for  the  frequency  with  which  medullary  cells  are  found 
in  the  cortex  and  cortical  cells  in  the  medulla. 

TECHNIC. 

(1)  Fix  the  simple  kidney  of  a  rabbit  or  guinea-pig  in  formalin-Muller's  fluid 
(technic  5,  p.  5).  Make  sections  through  the  entire  organ  including  the  papilla 
and  pelvis,  stain  with  haematoxylin-eosin  (technic  1,  p.  16),  and  mount  in  balsam. 
This  section  is  for  the  study  of  the  general  topography  of  the  kidney. 

(2)  Fix  small  pieces  from  the  different  parts  of  a  human  kidney  in  formalin- 
Miiller's  fluid  or  in  Zenker's  fluid.  Thin  sections  should  be  made,  some  cutting 
the  tubules  longitudinally,  others  transversely,  stained  with  hsematoxylin-eosin  and 
mounted  in  balsam. 

(3)  Blood-vessels. — For  the  purpose  of  demonstrating  blood-vessels  of  the 
kidney  the  method  of  double  injection  is  useful  (page  22). 

(4)  Ureter. —Cut  transversely  into  short  segments,  fix  in  formalin-J\Iiiller*s 
fluid  (technic  5,  p.  5),  and  stain  transverse  sections  with  hsematoxylin-eosin  (tech- 
nic 1,  p.  16),  or  with  hsematoxylin-picro-acid-fuchsin  (technic  3,  p.  16).  Mount  in 
balsam. 

(5)  Bladder  (technic  1,  p.  199,  or  technic  2,  p.  200).  By  the  latter  method  any 
desired  degree  of  distention  may  be  obtained. 

(6)  Adrenal.  Technic  same  as  (2)  above.  Thin  vertical  sections  should  in- 
clude both  cortex  and  medulla. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre,  vol.  iii. 

Gegenbauer:  Lehrbuch  der  Anatomie  des  Menschen,  vol.  ii. 

Henle  :  Handbuch  der  Anatomie  des  Menschen,  vol.  ii. 

Johnston  :  A  Reconstruction  of  a  Glomerulus  of  the  Human  Kidney.  Johns 
Hopkins  Hosp.  Bui.,  vol.  xi.,  1900. 

Miiller:  Ueber  die  Ausscheidung  des  Methylenblau  durch  die  Nieren. 
Deutsches  Archiv  f.  klin.  Med.,  Bd.  63,  1S99. 

Flint:  The  Blood-vessels,  Angiogenesis,  Organogenesis,  Reticulum  and  His- 
tology of  the  Adrenal.  Contributions  to  the  Science  of  Medicine,  Johns  Hopkins 
Press,  1900. 

Pfaundler :   Zur  Anatomie  der  Nebenniere.     Anzeiger  Akad.  Wien.  29,  1892. 

Nagel :  Ueber  die  Entwickelung  des  Urogenitalsystem  des  Menschen.  Arch. 
f.  Mik.  Anat.,  Bd.  xxxiv. 


CHAPTER    IX. 

THE    REPRODUCTIVE    SYSTEM. 

I.  MALE   ORGANS. 

The   Testis. 


The  testes  are  compound  tubular  glands.  Each  testis  is  enclosed 
in  a  dense  connective-tissue  capsule,  the  tunica  albuginea  (Fig.  173,  a). 
Outside  the  latter  is  a  closed  serous  sac,  the  tunica  vaginalis,  the 

visceral  layer  of  which  is  attached  to 
the  tunica  albuginea,  while  the  par- 
ietal layer  lines  the  inner  surface  of 
the  scrotum.  Posteriorly  the  serous 
sac  is  wanting,  the  testis  really  lying 
behind  and  outside  of  the  tunica 
vaginalis.  As  the  latter  is  derived 
from  the  peritoneum,  being  brought 
down  with  and  invaginated  by  the 
testes  in  their  descent  to  the  scrotum, 
it  is  lined  by  mesothelial  cells.  To 
the  inner  side  of  the  tunica  albuginea 
is  a  layer  of  loose  connective  tissue 
rich  in  blood-vessels,  the  tunica  vas- 
culosa.  Posteriorly  the  tunica  albu- 
ginea is  greatly  thickened  to  form  the 
corpus  Highmori,  or  mediastinum 
testis,  from  which  strong  connective- 
tissue  septa  radiate  (Figs.  173,  m  and 
174,  b).  These  septa  pass  complete- 
ly through  the  organ  and  blend  with 
the  tunica  albuginea  at  various  points. 
In  this  way  the  interior  of  the  testis 
is  subdivided  into  a  number  of  pyramidal  chambers  or  lobules,  with 
bases  directed  toward  the  periphery  and  apices  at  the  mediastinum 
(Figs.  173  and  174). 

Behind  the  testis  and  outside  of  its  tunica  albuginea  is  an  elon- 

270 


PlG.  173.  -Diagram  illustrating  the 
Course  and  Relations  of  the  Seminif- 
erous Tubules  and  their  Kxcretory 
Duets.  (Piersol.)  a,  Tunica  albuginea ; 
f>,  connective-tissue  septum  between 
lobules  ;  ;;/,  mediastinum  ;  /,  convo- 
luted portion  of  seminiferous  tubule  ; 
s,  straight  tubule;  r,  rete  testis;  e, 
vasa  efferentia;  c,  tubules  of  head  of 
epididymis;  lc\  vas  epididymis;  vd, 
vas  deferens;  va,  vas  aberrans  ;  />, 
paradidymis. 


THE  REPRODUCTIVE  SYSTEM 


271 


gated  body — the  epididymis  (Figs.  173,  c  and  1 74,  r),  consisting  of 
convoluted  tubules  continuous  with  those  of  the  mediastinum.  The 
epididymis   is  divided    into  e  a 

three    parts :    an    expanded  \      ^^_\      f^^~~ 

upper  extremity,  the  head 
or  globus  major  (Figs.  173 
and  174,6');  a  middle  piece, 
the  body  (Fig.  174,  d);  and 
a  slightly  expanded  lower 
extremity,  the  tail  or  globus 
minor.  From  the  last  named 
passes  off  the  main  excre- 
tory duct  of  the  testis,  the 
vas  deferens  (Fig.  173,  vd). 
All  of  the  tubules  of  the 
epididymis  are  continuous 
on  the  one  hand  with  the 
tubules  of  the  testicle,  and 
on  the  other  with  the  vas 
deferens.  They  thus  con- 
stitute a  portion  of  the  com- 
plex system  of  excretory 
ducts  of  the  testicle. 

The   seminiferous 
tubule  may  be  divided  with 

reference  to  structure  and  location  into  three  parts.  (1)  A  much 
convoluted  part,  the  convoluted  tubule,  which  begins  at  the  base  and 
occupies  the  greater  portion  of  a  lobule  of  the  testis.  As  they 
approach  the  apex  of  a  lobule  several  of  these  convoluted  tubules 
unite  to  form  (2)  the  straiglit  tubule.  This  passes  through  the  apex  of 
the  lobule  to  the  mediastinum,  where  it  unites  with  other  straight 
tubules  to  form  (3)  the  irregular  network  of  tubules  of  the  medias- 
tinum, the  rete  testis  (Fig.  177,  c). 

1.  The  Convoluted  Tubule. — This,  which  may  be  considered 
the  most  important  secreting  portion  of  the  lobule,  since  it  is  here 
that  the  spermatozoa  are  formed,  has  a  diameter  of  from  1  50  to  250,". 
The  tubules  begin,  some  blindly,  others  by  anastomoses  with  neigh- 
boring tubules,  near  the  periphery  of  the  lobule,  and  pursue  a  tortuous 
course  toward  its  apex  (Fig.   177,  a). 


Fig.  174.  —Longitudinal  Section  through  Human  Testis 
and  Epididymis.  X  2.  (Bohm  and  von  Davidoff.) 
The  light  strands  are  connective-tissue  septa.  <.i, 
Tunica  albuginea  ;  b,  mediastinum  and  rete  testis  ; 
c,  head  of  epididymis  ;  d,  body  of  epididymis  ;  e,  lob- 
ule ;  5,  straight  tubules  :  /,  vas  epididymis. 


2/2 


THE   ORGANS. 


The  wall  of  the  convoluted  tubule  (Fig.  175)  consists  of  three 
layers  :  (a)  An  outer  layer  composed  of  several  rows  of  flattened 
connective-tissue  cells  which   closely  invest  the  tubule;    (/>)  a  thin 


Fig.  175. — Cross  Section  of  Convoluted  Portion  of  Human  Seminiferous  Tubule.  X  480.  (Kolli- 
ker.j  M,  Basement  membrane  ;  z,  its  inner  homogeneous  layer,  fs,  its  outer  fibrous  layer  ; 
5,  nucleus  of  Sertoli  cell  ;  sf>,  spermatogone  ;  sc,  spermatocyte  ;  sc',  spermatocyte  showing 
mitosis  ;  sf,  nearly  mature  spermatozoon  ;  sf,  spermatozoon  free  in  lumen  of  tubule  ;  d, 
degenerating  nucleus  in  lumen  :  /",  fat  droplets  stained  by  osmic  acid. 


basement  membrane  ;  and  (c)  a  lining  epithelium.  The  epithelium 
consists  of  two  kinds  of  cells,  the  so-called  supporting  ox  sustentacula,!' 
cells  and  the  glandular  cells  proper,  the  spermatogenic  cells. 

The  sustcntacular  cells,  or  columns  of  Sertoli,  are  irregular,  high, 
epithelial  structures,  whose  bases  rest  upon  the  basement  membrane, 
and  which  extend  through  or  nearly  through  the  entire  epithelium 
(Fig.  1  76,  s).  Their  sides  show  marked  irregularities  and  depressions, 
due  to  the  pressure  of  surrounding  spermatogenic  cells.  The  cells 
of  Sertoli  were  long  considered  as  sustentacular  in  character.  It  has 
recently  been  suggested  that  these  cells  are  derived  from  the  sper- 
matogonia,  but  that,  instead   of  developing   into   spermatozoa,  they 


THE  REPRODUCTIVE  SYSTEM.  273 

undergo  retrograde  changes,  their  protoplasm  mingling  with  the 
intercellular  substance,  their  nuclei  becoming  lost  and  the  cells 
finally  disappearing.  According  to  this  theory  the  tuft-like  arrange- 
ment of  the  spermatozoa  about  the  ends  of  the  Sertoli  cells  is  due 
to  pressure   by  surrounding  spermatogenic   cells  (Figs.    176,  h  and 

178,  /)• 

The  appearance  which  the  spermatogenic  cells  present  depends 
upon  the  functional  condition  of  the  tubule.  In  the  resting  state 
the  epithelium  consists  of  several  layers  of  spherical  cells  containing 

h  f 

\ / 


mm®/ 


//                      s                6 

\. ..... ,  .   \      1 

till!!! 

1! 

'.   -     !    ■  I   '.■'''..   £ 

^.'kWZ  ■  / 


>sp 


stcj: 


■J 


•h 


sf 


Fig.  176. — Parts  of  Transverse  Section  of  three  Seminiferous  Tubules  from  Testis  of  White 
Mouse.  X  600.  (Szymonowicz.)  .?,  Sertoli  cell  with  nucleus;  sp,  spermatogone,  resting 
state;  sp'.  spermatogone  in  mitosis  ;  sc,  spermatocj-te  ;  st,  spermatid  ;  sf,  spermatid  de- 
veloping into  spermatozoon  ;  //,  head  of  spermatozoon  ;  /,  tails  of  developing  spermato- 
zoa ;  b,  blood-vessel  ;  c,  interstitial  cell  ;  ;;/,  basal  membrane  ;_/",  fat  droplets. 

nuclei  which  stain  with  varying  degrees  of  intensity.  In  the  active 
state  several  distinct  layers  of  spermatogenic  cells  can  be  differen- 
tiated.    These  from  without  inward  are  as  follows : 

( 1)  Spermatogones  (Figs.  1 75  and  1 76,  sf>). — These  are  small  cuboi- 

dal  cells  which  lie  against  the  basement  membrane.      Their  nuclei  are 
iS 


'4 


THE   ORGAXS. 


spherical  and  rich  in  chromatin.      By  mitotic  division  of  the  sperma- 
togones are  formed  the  cells  of  the  second  layer,  the  spermatocytes. 

(2)  Spermatocytes  (Figs.  175  and 
176,  se). — These  are  larger  spherical 
cells  with  abundant  cytoplasm  and 
large  vesicular  nuclei  showing  vari- 
ous stages  of  mitosis.  They  form  from 
two  to  four  layers  to  the  inner  side  of 
the  spermatogones,  and  are  sometimes 
differentiated  into  spermatocytes  of  the 


~  ... 


i0—* 


Fig. 


177. 


Fig.  178. 


Fig.  177.— Passage  of  Convoluted  Part  of  Seminiferous  Tubules  into  Straight  Tubules  and 
of  these  into  the  Rete  Testis.  (Milhalkowicz.)  <?,  Convoluted  part  of  tubule;  /',  fibrous 
stroma  continued  from  the  mediastinum  testis;  c,  rete  testis. 

PlG.  17?;.  — Spermatoblast  with  some  Adjacent  Sperm  Cells,  from  Testis  of  Sparrow.  (From 
Kolliker,  after  Etzold.)  M,  Basement  membrane;  .r,  nucleus  of  Sertoli  cell  ;  s/>,  sperma- 
togones; sc,  spermatocyte  ;  s/:  and  s/%,  spermatids  lying  along  the  surface  of  the  Sertoli 
cell,  s'  and  sl3  ;  at  s/s  are  seen  the  nearly  mature  spermatozoa  ; /,  tuft-like  arrangement 
of  bodies  of  spermatids  around  free  end  of  Sertoli  cell,  with  two  mature  spermatozoa. 


first  order  and  spermatocytes  of  the  second  order.     By  mitotic  division 
of  the  innermost  spermatocytes  are  formed  the  spermatids. 

(3)  The  spermatids  (Figs.  175  and  176,  si)  are  small  round  cells 
which  line  the  lumen  of  the  seminiferous  tubule.  They  arc  the 
direct  progenitors  of  the  spermatozoa.  (For  details  of  spermatogen- 
esis see  page  281.) 


THE  REPRODUCTIVE  SYSTEM.  275 

In  the  actively  secreting  testicle  spermatozoa  are  frequently  found 
either  free  in  the  lumen  of  the  tubule  or  with  their  heads  among  the 
superficial  cells  and  their  tails  extending  out  into  the  lumen  (Figs. 
175,  sf1  and  178). 

Separating  and  supporting  the  convoluted  tubules  is  a  small 
amount  of  interstitial  connective  tissue  in  which  are  the  blood-ves- 
sels and  nerves.     Among  the  usual  connective-tissue  elements  are 

■  -dff 


M.'f  ;', ,  o  v*  ■J"'T. ,  .■:lf^,j:'>'V'"*'    'V  .cS-"„s --v."  ''    <     *v7*  ■ ;  "        ~^'.v\F'v .  r^T  "     v 

.<  "  V  •;.■■"//  ■'/■-■•  ■:  '■ x •■',• ■■■Ki%  ;•.  _V;  *^'S*'W--~^U^..<*.-4^V''  /•■*.•.< r<-s=-..^, 

' "'  '  J£ 

FlG.  179.— From  Section  through  Human  Mediastinum  and  Rete  Testis.  X  96.  (Kolliker.)  ^4,  Ar- 
tery ;  F,  vein  ;  L,  lymph  space  ;  C,  canals  of  rete  testis  ;  s,  cords  of  tissue  projecting-  into 
the  lumina  of  the  tubules  and  so  cut  transversly  or  obliquely  ;  Si,  section  of  convoluted 
portion  of  seminiferous  tubule. 

found  groups  of  rather  large  spherical  cells  with  large  nuclei — inter- 
stitial cells.  They  are  believed  to  represent  remains  of  the  Wolffian 
body  (Fig.  176,  e). 

2.  The  Straight  Tubule. — With  the  termination  of  the  con- 
voluted   portion,   the    spermatogenic   tissue   of   the   gland  ends,   the 


76 


THE   ORGANS. 


^ 


FIG.  iJSo.—  Part  of  a  Cross  Section  through  a  Vas 
Efferens  of  the  Human  Epididymis.  X  140. 
(Kolliker.)  F,  High  columnar  ciliated  epithe- 
lium ;  d,  lower  non-ciliated  epithelium,  present- 
ing appearance  of  a  gland  ;  d',  the  same  cut 
obliquely. 


remainder  of  the  tubule  constituting  a  complex  system  of  excretory 
ducts.     The  straight  tubule  is   much   narrower  than  the  convoluted, 

having  a  diameter  of  from  20 
to    40  p.      It   is    lined    by    a 
single  layer  of  cuboidal  cells 
resting  upon  a  thin  basement 
membrane.     At   the  apex  of 
the  lobule  the  straight  tub- 
ules become  continuous  with 
the  tubules  of  the  rete  testis. 
3.  The  Tubules  of  the 
Rete     Testis. — These     are 
irregular    canals    which  vary 
greatly    in     shape    and    size. 
They  are  lined  with  a  single  layer  of   low  cuboidal  or  flat  epithelial 
cells  (Fig.  179,  C). 

The  Seminal  Ducts. — While  the  already  described  straight 
tubules  and  the  tubules  of  the  rete  testis  must  be  regarded  as  part 
of  the  complex  excretory  duct  system  of  the  testis,  there  are  certain 
structures  which  are  wholly  outside  the  testis  proper,  which  serve  to 
transmit  the  secretion  of  the  testis,  and  are  known  as  the  seminal 
ducts.  On  leaving  the  testis  these  ducts  form  the  epididymis,  after 
which  they  converge  to  form  the  main  excretory  duct  of  the  testis, 
the  vas  deferens. 

The  Epididymis. — From  the  tubules  of  the  rete  testis  arise  from 
eight  to  fifteen  tubules,  the  vasa  efferentia,  or  efferent  ducts  of  the 
testis  (Fig.  173,  e).  Each  vas  efferens  pursues  a  tortuous  course,  is 
separated  from  its  fellows  by  connective  tissue,  and  forms  one  of  the 
lobules  of  the  head  of  the  epididymis.  The  epithelium  of  the  vasa 
efferentia  consists  of  two  kinds  of  cells,  high  columnar  ciliated  cells 
(Fig.  180,  F),  and,  interspersed  among  these,  low  cuboidal  non- 
ciliated  cells  (Fig.  180,  d).  Occasionally  some  of  the  high  cells  are 
free  from  cilia  and  some  of  the  cuboidal  cells  may  bear  cilia.  The 
cuboidal  cells  lie  in  groups  between  groups  of  the  higher  cells,  often 
giving  the  appearance  of  crypt-like  depressions.  These  have  been 
referred  to  as  intraepithelial  glands.  They  do  not,  however,  invagi- 
nate  the  underlying  tissues.  The  epithelium  rests  upon  a  basement 
membrane,  beneath  which  are  several  layers  of  circularly  disposed 
smooth  muscle  cells. 


THE  REPRODUCTIVE  SYSTEM.  277 

The  vasa  efferentia  converge  to  form  the  vas  epididymis  (Fig. 
181).  Here  the  epithelium  is  of  the  stratified  variety,  there  being 
two  or  three  rows  of  cells.  The  surface  cells  are  narrow,  high,  and 
ciliated,  and  their  nuclei  are  placed  at  different  levels  (Fig.  182).  The 
cilia  are  long  and  each  cell  has  only  a  few  cilia.  The  deeper  cells 
are  irregular  in  shape.  The  basement  membrane  and  muscular  layers 
are  the  same  as  in  the  vasa  efferentia.  As  the  vas  deferens  is  ap- 
proached the  muscular  coat  becomes  thickened,  and  is  sometimes 
strengthened  by  the  addition  of  scattered  bundles  of  longitudinally 
disposed  cells. 

The  Vas  Deferens. — The  walls  of  the  vas  deferens  consist  of 
four  coats — mucosa,  submucosa,  muscularis,  and  fibrosa  (Fig.  183). 

The  mucosa  is  folded  longitudinally,  and  is  composed  of  a  stroma 
and  a  lining  epithelium.  The  epithelium  is  of  the  stratified  columnar 
type  with  two  or  three  rows  of  cells,  being  similar  to  that  lining  the 
vas  epididymis.  The  extent  to  which  the  epithelium  is  ciliated  va- 
ries greatly.     In  some  cases  the  entire  vas  is  ciliated,  in  others  only 


m 
Fig.  181.— From  Cross  Section  through  Head  of  Epididymis.   X  35.   (Kolliker.)    />,  Interstitial 
connective  tissue  ;  c,  sections  through  tubules  of  epididymis,  showing  two-layered  colum- 
nar epithelium  ;  g,  blood-vessel. 

the  upper  portion,  in  still  others  no  cilia  are  present  beyond  the 
epididymis.  The  epithelium  rests  upon  a  basement  membrane  be- 
neath which  is  a  fibro-elastic  cellular  stroma.  The  stroma  merges 
without  distinct  demarcation  into  the  more  vascular  submucosa. 

The    muscularis   consists    of    two   strongly  developed   layers    of 


i 


•w^'v 


2;8  THE  ORGANS. 

smooth  muscle,  an  inner  circular  and  an  outer  longitudinal  (Fig.  183), 
which  together  constitute  about  seven-eighths  of  the  wall  of  the  vas. 
At  the  beginning  of  the  vas  deferens  a  third  layer  of  muscle  is  added 

composed  of  longitudinal  bundles, 

'//  and  situated  between   the  inner 

;"^^-^=^^_^  ^^^  ^.w^rr — ''        circular  layer  and  the  submucosa. 

The,  fibrosa  consists  of  fibrous 
tissue  containing  many  elastic 
fibres.  1 

Near  its  termination  the  vas 
dilates  to  form  the  ampulla,  the 
walls  of  which  present  essential- 
ly the  same  structure  as  those  of 
the  vas.  The  lining  epithelium 
action  through  Wail  of      ■     however,  frequently  markedly 

Tubules  of  Epididymis.    X  700.    (kolhker.)  x  J  ■> 

<Fig.  1S1  more  highly  magnified.)     f>,  Con-        pigmented    and    the    milCOSa    COll- 
nective-tissue  and  smooth  muscle  cells ;  e,  .  .  .       .         .      ,  .         . 

basal  layer  of  epithelial  ceils;/,  high  coi-      tarns  branched  tubular  glands. 

umnar  epithelial    cells;   /.  pigment  gran-  f^e      Seminal     VesideS      and 

ules  in  columnar  cells  ;  c.  cuticula  ;  //,  cilia. 

Ejaculatory  Ducts. — The  sem- 
inal vesicles.  The  walls  of  the  seminal  vesicles  are  similar  in  structure 
to  those  of  the  ampulla.  The  epithelium  is  pseudo-stratified  with 
two  or  three  rows  of  nuclei  and  contains  a  yellow  pigment.  When 
the  vesicles  are  distended  the  epithelium  flattens  out  and  the  nuclei 
lie  more  in  one  plane,  thus  giving  the  appearance  of  an  ordinary  sim- 
ple columnar  epithelium.  Beneath  the  epithelium  is  a  thin  stroma, 
outside  of  which  is  an  inner  circular  and  an  outer  longitudinal  layer 
of  smooth  muscle,  both  layers  being  much  less  developed  than  in  the 
vas.  The  seminal  vesicles  are  to  be  regarded  as  accessory  genital 
glands. 

The  ejaculatory  ducts  are  lined  with  a  single  layer  of  columnar 
cells.  The  muscularis  is  the  same  as  in  the  ampulla  except  that  the 
inner  circular  layer  is  thinner.  In  the  prostatic  portion  of  the  duct 
the  muscularis  is  indistinct,  merging  with  the  muscle  tissue  of  the 
gland.  The  ducts  empty  either  directly  into  the  ureter  or  into  the 
ureter  through  the  vesicula  prostatica. 

Rudimentary  Structures  Connected  with  the  Development  of 
the  Genital  System.  -Connected  with  the  testicle  and  its  ducts  are 
remains  of  certain  foetal  structures.      These  are: 

(1)  The  paradidymis ;  or  organ  of  Giraldes,  situated  between  the 


THE  REPRODUCTIVE   SYSTEM.  279 

vessels  of  the  spermatic  cord  near  the  testis.      It  consists  of  several 
blind  tubules  lined  with  simple  columnar  ciliated  epithelium. 

(2)  The  ductus  aberrans  Hallcri,  found  in  the  epididymis.  It  is 
lined  with  simple  columnar  ciliated  epithelium  and  opens  into  the 
vas  epididymis.  Instead  of  a  single  ductus  aberrans,  several  ducts 
may  be  present. 

(3)  The  appendix  testis  (stalked  hydatid  or  hydatid  of  Morgagni), 
in  the  upper  part  of  the  globus  major.  It  consists  of  a  vascular 
connective  tissue  surrounding  a  cavity  lined  with  simple  columnar 
ciliated  epithelium. 

(4)  The  appendix  cpididymidis,  a  vascular  structure,  not  always 
present,  lying  near  the  appendix  testis.  It  resembles  the  latter  in 
structure. 


--/ 


■     r  V    - --    -   -  •       ;  f  jry.. .  ■»  :       ■    ■-- 


I ','? 


^SBflBHs^ 


-  .  .    '^-"°:,  •■  "Js 

FIG.  183. — Cross  Section  of  Human  Vas  Deferens.  X  37.  (Szymonowicz.)  a,  Epithelium  ;  h, 
stroma  ;  c,  submucosa  ;  d,  inner  circular  muscle  layer  ;  e,  outer  longitudinal  muscle  layer  ; 
y,  fibrotis  layer  ;  g,  blood-vessels. 

The  paradidymis  and  ductus  aberrans  Halleri  probably  represent 
remains  of  the  embryonal  mesonephros.  The  appendix  testis  and  the 
appendix  epididymidis  are  believed  by  some  to  be  derived  from  the 
primitive  kidney,  by  others  from  the  embryonal  duct  of  Mliller. 

Blood-vessels. — Branches  of  the  spermatic  artery  ramify  in  the 
mediastinum  and  in  the  tunica  vasculosa.      These  send  branches  into 


2 'So  THE  ORGANS. 

the  septa  of  the  testicle,  which  give  rise  to  a  capillary  network  among 
the  convoluted  tubules.  From  the  capillaries  arise  veins  which  ac- 
company the  arteries. 

Lymph  capillaries  begin  as  clefts  in  the  tunica  albuginea  and  in 
the  connective  tissue  surrounding  the  seminiferous  tubules.  These 
connect  with  the  more  definite  lymph  vessels  of  the  mediastinum  and 
of  the  spermatic  cord. 

Nerves. — Non-medullated  nerve  fibres  form  plexuses  around  the 
blood-vessels.  From  these,  fibres  pass  to  plexuses  among  the  semi- 
niferous tubules.  Their  exact  method  of  termination  in  connection 
with  the  epithelium  has  not  been  determined.  In  the  epididymis  are 
found  small  sympathetic  ganglia.  The  walls  of  the  vasa  efferentia, 
vas  epididymis,  and  vas  deferens  contain  plexuses  of  non-medullated 
nerve  fibres,  which  give  off  terminals  to  the  smooth  muscle  cells  and 
to  the  mucosa. 

The  Spermatozoa. — The  spermatozoa  are  the  specific  secretion 
of  the  testicle.  They  are  long,  slender  flagellate  bodies,  from  50  to 
70  >).  in  length,  and  are  suspended  in  the  semen,  which  is  a  secretion 
of  the  accessory  sexual  glands.  It  has  been  estimated  that  the  human 
spermatozoa  average  about  sixty  thousand  per  cubic  millimetre  of 
semen. 

The  human  spermatozoon  consists  of  (1)  a  head,  (2)  a  middle 
piece  or  body,  and  (3)  a  tail  or  flagellum  (Fig.  184). 

The  head,  from  3  to  5  //  long  and  about  half  that  in  breadth,  is 
oval  in  shape  when  seen  on  flat,  pear-shaped  when  seen  on  edge. 
It  consists  of  chromatin  derived  from  the  nucleus  of  the  parent 
cell. 

The  body  is  cylindrical,  about  the  same  length  as  the  head,  and 
consists  of  a  fibrillated  central  core,  the  axial  thread,  surrounded  by 
a  protoplasmic  capsule.  Just  behind  the  head  the  axial  thread  pre- 
sents a  bulbous  thickening,  the  terminal  nodule  or  end  bulb,  which 
fits  into  a  depression  in  the  head.  The  terminal  nodule  probably 
represents  the  centrosome. 

The  tail  consists  of  a  main  segment,  from  40  to  60,".  in  length, 
and  a  terminal  segment  having  a  length  of  from  5  to  10  //..  The  main 
segment  has  a  central  fibrillated  axial  thread  which  is  continuous 
with  the  axial  thread  of  the  body.  This  is  enclosed  in  a  thin  mem- 
brane or  capsule  continuous  with  the  capsule  of  the  body.  The 
terminal  segment  consists  of  the  axial  thread  alone.     The  motility  of 


THE  REPRODUCTIVE  SYSTEM. 


281 


the  spermatozoon  depends  entirely  upon  the  flagellate  movements  of 
the  tail.  In  many  of  the  lower  animals  the  spermatozoon  has  a  much 
more  complicated  structure. 

Of  the  above-described  parts  of  the  spermatozoon  only  the  head  and 
tail  can  tisually  be  differentiated,  except  by  the  use  of  special  methods 
and  very  high-poiver  objectives. 

Development  of  the  Spermatozoa. — As  already  noted  in  de- 
scribing the  testicle,  the  spermatozoa  are  developed  from  the  epithe- 
lial cells  of  the  seminiferous  tubules.  The  most  peripheral  of  the 
tubule  cells,  the  spermatogones  (Fig.  175,  sp  and 
Fig.  176,  sf)  are  small  round  cells  with  nuclei  rich 
in  chromatin.  By  mitosis  the  spermatogone  gives 
rise  to  two  daughter  cells,  one  of  which  remains  at 
the  periphery  as  a  spermatogone,  while  the  other 
takes  up  a  more  central  position  as  a  spermatocyte 
(Fig.  176,  sc  and  Fig.  178,  sc).  The  latter  are 
rather  large  spherical  cells,  whose  nuclei  show  very 
distinct  chromatin  networks.  By  mitotic  division 
of  the  spermatocytes  of  the  innermost  row  are 
formed  the  spermatids  (Fig.  176,  st  and  Fig.  178,  sf). 
These  are  small  spherical  cells,  which  line  the 
lumen  of  the  tubule  and  are  the  direct  progenitors 
of  the  spermatozoa.  In  the  transformation  of  sper- 
matocyte into  spermatid  an  extremely  important 
change  takes  place  in  the  nucleus.  This  consists 
in  a  reduction  of  its  chromosomes  to  one-half  the 
number  specific  for  tJie  species  (page  42).  The  trans- 
formation of  the  spermatid  into  the  spermatozoon 
differs  somewhat  in  different  animals  and  the  de- 
tails of  the  process  must  be  regarded  as  not  yet 
definitely  determined.  The  nucleus  of  the  sper- 
matid first  becomes  oval  in  shape,  and  its  chromosomes  become 
condensed  into  a  small  homogeneous  mass,  which  forms  the  head 
of  the  spermatozoon.  During  their  transformation  into  the  heads 
of  the  spermatozoa,  the  nuclei  of  the  spermatids  arrange  them- 
selves in  tufts  against  the  inner  ends  of  the  cells  of  Sertoli.  This 
compound  structure,  consisting  of  a  Sertoli  cell  and  of  a  group  of 
developing  spermatozoa  attached  to  its  central  end,  is  known  as  a 
spermatoblast  (Fig.   178).      The  body  or  middle  piece  of  the  sperma- 


FlG. 


■Human 


Spermatozoa.  (.Af- 
ter Retzius.)  /, 
Head  seen  on  flat  ; 
2,  head  seen  on 
edge  ;  k,  head  ;  w. 
body  ;  /.  tail ;  e,  end 
piece. 


2S2  THE   ORGANS. 

tozoon  is  described  by  most  investigators  as  derived  from  the  centro- 
some,  while  the  tail  is  a  derivative  of  the  cytoplasm. 

TECHNIC. 

(i)  For  the  study  of  the  general  topography  of  the  testis,  remove  the  testis  of 
a  new-born  child,  make  a  deep  incision  through  the  tunica  albuginea  in  order  to 
allow  the  fixative  to  penetrate  quickly,  and  fix  in  formalin-M tiller's  fluid  (technic  5, 
p.  5).  Antero-posterior  longitudinal  sections  through  the  entire  organ  and  in- 
cluding the  epididymis  should  be  stained  with  hamiatoxylin-picro-acid-fuchsin 
itechnic  3.  p.  16)  or  with  hrematoxylin-eosin  (technic  1,  p.  16)  and  mounted  in 
balsam. 

(2)  The  testis  of  a  young  adult  is  removed  as  soon  after  death  as  possible,  is 
cut  into  thin  transverse  slices,  which  include  the  epididymis,  and  is  fixed  in  forma- 
lin-Midler's or  in  Zenker's  fluid  (technic  9,  p.  6).  Select  a  slice  which  includes 
the  head  of  the  epididymis,  cut  away  the  anterior  half  or  two-thirds  of  the  testis 
proper  in  order  to  reduce  the  size  of  the  block,  and,  after  the  usual  hardening  and 
embedding,  cut  thin  sections  through  the  remaining  posterior  portion  of  the  testis, 
the  mediastinum  and  epididymis.  Stain  with  haematoxylin-eosin  (technic  1,  p. 
16)  and  mount  in  balsam. 

(3)  For  the  study  of  spermatogenesis  fix  a  mouse's  testis  in  chrome-acetic- 
osmic  mixture  (technic  7,  p.  6).  Harden  in  alcohol  and  mount  thin  unstained 
sections  in  balsam  or  in  glycerin. 

(4;  Spermatozoa.  — Human  spermatozoa  may  be  examined  fresh  in  warm  nor- 
mal saline  solution  or  fixed  in  saturated  aqueous  solution  of  picric  acid  and 
mounted  in  glycerin.  Mammalian  spermatozoa  may  be  obtained  from  the  vagina 
after  intercourse,  or  by  incision  into  the  head  of  the  epididymis.  Technic  same  as 
for  human. 

(5)  A  portion  of  the  vas  deferens  is  usually  removed  with  the  testis  and  may 
be  subjected  to  technic  (2)  above.  Transverse  sections  are  stained  with  haema- 
toxylin-eosin and  mounted  in  balsam. 

The   Prostate  Gland. 

The  prostate  is  described  by  some  as  a  compound  tubular,  by 
others  as  a  compound  alveolar  gland.  It  is  perhaps  best  regarded 
as  a  collection  of  simple  branched  tubular  glands  with  dilated  termi- 
nal tubules.  These  number  from  forty  to  fifty,  and  their  ducts  con- 
verge to  form  about  twenty  main  ducts,  which  open  into  the  urethra. 
The  gland  is  surrounded  by  a  capsule  of  fibro-elastic  tissue  and 
smooth  muscle  cells,  the  muscle  cells  predominating.  From  the 
capsule  broad  trabecule  of  the  same  structure  as  the  capsule  pass  into 
the  gland.  The  amount  of  connective  tissue  is  large.  It  is  less  in 
tin-  prostate  of  the  young  than  of  the  old.  The  hypertrophied  pros- 
tate of  age  is  due  mainly  to  an  increase  in  the  connective-tissue  ele- 
ments.     The  tubules  have  wide   lumina  and   are   lined  with   simple 


THE  REPRODUCTIVE  SYSTEM.  283 

cuboidal  epithelium  of  the  serous  type,  resting  upon  a  delicate  base- 
ment membrane  (Fig.  185).  Less  commonly  the  epithelium  is 
pseudo- stratified.  The  ducts  are  lined  with  simple  columnar  epithe- 
lium until  near  their  terminations,  where  they  are  lined  with  trans- 
itional epithelium  similar  to  that  lining  the  urethra.      Peculiar  con- 


.vv 


"S  '  ■!//.'.    • 


*&& 


.  .'^'v 


si   y 


„/■  f 


'•■*'■■/' \  ■'.  ;'£       „>'"'-•■-  ■*"'.■' v-  '■■■ :  f  '"'.'•■■■'  '-.;•-"*  -■-'" 


Fig.  185. —Section  of  Human  Prostate.    X  150.     (Technic  i,  p.  284.)     a,  Epithelium  of  tubule: 
S,  interstitial  connective  tissue  ;  c,  corpora  amj-lacea. 

centrically  laminated  bodies,  crescentic  corpuscles,  or  corpora  amylacea, 
are  frequently  present  in  the  terminal  tubules  (Fig.  185,  c).  They 
are  more  numerous  after  middle  life. 

Through  the  prostate  runs  the  prostatic  portion  of  the  urethra. 

Within  the  prostate  is  found  the  vesicula  prostatica  {iitricidus 
prostaticus — uterus  masculinus).  It  represents  the  remains  of  a  foe- 
tal structure,  the  Mullerian  duct  (see  page  310)  and  consists  of  a 
blind  sac  with  folded  mucous  membrane  lined  with  a  two-rowed 
ciliated  epithelium  which  dips  down  to  form  short  tubular  glands. 
The  prostatic  secretion  is  serous. 

The  blood-vessels  of  the  prostate  ramify  in  the  capsule  and  tra- 
becular. The  small  arteries  give  rise  to  a  capillary  network  which 
surrounds  the  gland  tubules.  From  these  arise  small  veins,  which 
accompany  the  arteries  in  the  septa  and  unite  to  form  venous  plexuses 
in  the  capsule. 


284  THE  ORGANS. 

The  lymphatics  begin  as  blind  clefts  in  the  trabecule  and  follow 
the  general  course  of  the  blood-vessels. 

Nerves. — Small  groups  of  sympathetic  ganglion  cells  are  found  in 
the  larger  trabeculae  and  beneath  the  capsule.  Axones  of  these  cells 
pass  to  the  smooth  muscle  of  the  trabeculae  and  of  the  walls  of  the 
blood-vessels.  Their  mode  of  termination  is  not  known.  Timofeew 
describes  afferent  niedullated  fibres  ending  within  capsular  structures 
of  flat  nucleated  cells.  Two  kinds  of  fibres  pass  to  each  capsule : 
one  a  large  medullated  fibre  which  loses  its  sheath  and  gives  rise 
within  the  capsule  to  several  flat  fibres  with  serrated  edges,  the  other 
small  medullated  fibres  which  lose  their  sheaths  and  split  up  into 
small  varicose  fibrils  which  form  a  network  around  the  terminals  of 
the  larger  fibre. 

Cowper's   Glands. 

The  bulbo-urethral  glands,  or  glands  of  Cowper,  are'  small, 
branched,  tubular  glands.  They  are  lined  with  mucous  cells.  The 
smaller  ducts  are  lined  with  simple  cuboidal  epithelium.  They  unite 
to  form  two  main  excretory  ducts  which  open  into  the  urethra  and 
are  lined  with  stratified  columnar  epithelium  consisting  of  two  or 
three  layers  of  cells. 

TECHNIC. 

(i)  Fix  small  pieces  of  the  prostate  of  a  young  man  in  formalin-Miiller's  fluid 
(teclinic  5,  p.  5).  Stain  sections  with  haematoxylin-eosin  (technic  1.  p.  (6)  and 
mount  in  balsam. 

(2)  The  prostate  of  an  old  man  should  be  treated  with  the  same  technic  and 
compared  with  the  above. 

(3)  Cowper's  glands.     Same  technic  as  prostate  (1). 

The   Penis. 

The  penis  consists  largely  of  three  long  cylindrical  bodies,  the 
corpus  spongiosum  and  the  two  corpora  cavernosa.  The  latter  lie  side 
by  side,  dorsally,  while  the  corpus  spongiosum  occupies  a  medial 
ventral  position  (Fig.  186).  All  three  are  enclosed  in  a  common 
connective-tissue  capsule  which  is  loosely  attached  to  the  overlying 
skin.  In  addition  each  corpus  has  its  own  special  capsule  or  tunica 
albuginca,  about  a  millimetre  in  thickness,  and  composed  of  dense 
connective  tissue  containing  many  elastic  fibres. 

The  corpus  spongiosum  and  corpora  cavernosa  have  essentially  the 


THE  REPRODUCTIVE  SYSTEM. 


285 


same  structure,  being  composed  of  so-called  erectile  tissue  (Fig.  187;. 
This  consists  of  thick  trabecular  of  intermingled  fibro-elastic  tissue 
and  bundles  of  smooth  muscle 
cells,  which  anastomose  to  form 
a  coarse- meshed  network,  the 
spaces  of  which  are  lined  with 
endothelium.  The  spaces  are 
known  as  cavernous  sinuses,  and 
communicate  with  one  another, 
and  with  the  blood-vessels  of 
the  penis.  In  the  flaccid  con- 
dition of  the  organ  these  sinuses 
are  empty  and  their  sides  are  in 
apposition.       In 

sinuses  become  filled  with  venous 
blood. 


erection  these  FIG.  186.— Transverse  Section  through  Human 
Penis,  a,  Skin;  6,  subcutaneous  tissue;  c, 
fibrous  tunic  ;  d,  dorsal  vein  ;  e,  corpora  cav- 
ernosa ;  f,  corpus  spongiosum  ;  ,?,  urethra. 


The  arteries  have  thick  muscular  walls  and  run  in  the  septa.  A 
few  of  them  open  directly  into  the  venous  sinuses.  Most  of  them 
give  rise  to  a  superficial  capillary  network  beneath  the  tunica  albu- 
ginea.     From  this  capillary  plexus  the  blood  passes  into  a  plexus  of 

.  .  .         ■  ■  :  .&•  '  '» 


Fig.  187.— Erectile  Tissue  of  Corpus  Spongiosum  of  Human  Penis.  X  60.  a,  Trabeculae  of  con- 
nective tissue  and  smooth  muscle  ;  b,  cavernous  sinuses  ;  c,  groups  of  leucocytes  in  sinus. 

broader  venous  channels  in  the  periphery  of  the  erectile  tissue,  and 
these  in  turn  communicate  with  the  cavernous  sinuses.  The  usual 
direct  anastomoses  between  arterial  and  venous  capillaries  also  occur. 


2  86  THE  ORGANS. 

The  blood  may  therefore  pass  either  through  the  usual  course — arte- 
ries, capillaries,  veins — or,  under  certain  conditions,  may  pass  through 
the  cavernous  sinuses.  This  determines  the  flaccid  or  the  erect  con- 
dition of  the  organ.  The  veins  arise  partly  from  the  capillaries  and 
partly  from  the  cavernous  sinuses.  They  pass  through  the  tunica 
albugineaand  empty  into  the  dorsal  vein  of  the  penis  (Fig.  186).  In 
the  corpus  spongiosum  there  is  probably  no  direct  opening  of  arteries 
into  the  sinuses.      Both  trabecule  and  sinuses  are  also  smaller. 

Of  the  lymphatics  of  the  penis  little  definite  is  known. 

The  nerve  endings,  according  to  Dogiel,  consist  of  :  (a)  free  sensory 
endings,  {b)  deeply  situated  genital  corpuscles,  (c)  Pacinian  corpus- 
cles and  Krause's  end-bulbs  in  the  more  superficial  connective  tissue, 
and  (a7)   Meissner's  corpuscles  in  the  papillae.     (For  details  see  pages 

348,  349,  antl  350. 

The  glans  penis  consists  of  erectile  tissue  similar  in  structure  to 
that  of  the  corpus  cavernosum,  except  that  the  venous  spaces  are 
smaller  and  more  regular.  The  mucous  membrane  is  very  closely  at- 
tached to  the  fibrous  sheath  of  the  underlying  erectile  tissue.  A  few 
small  sebaceous  glands,  unconnected  with  hairs — the  glands  of  Tyson 
— are  found  in  the  mucous  membrane  of  the  base  of  the  glans 
(corona). 

The  prepuce  is  a  fold  of  skin  which  overlies  the  glans  penis.  Its 
inner  surface  is  lined  with  mucous  membrane. 

The   Urethra.1 

The  male  urethra  is  divided  into  three  parts — prostatic,  mem- 
branous, and  penile.  The  wall  of  the  urethra  consists  of  three  coats 
— mucous,  submucous,  and  muscular.  The  structure  of  the  wall 
differs  in  the  different  parts  of  the  urethra. 

The  mucous  membrane  (Fig.  188)  consists  of  epithelium  and 
stroma.  The  epithelium  of  the  prostatic  part  is  stratified  squamous 
(transitional),  resembling  that  of  the  bladder.  In  the  membranous 
part  it  is  stratified  columnar  or  pseudostratified.  In  the  penile  por- 
tion it  is  pseudostratified  up  to  the  fossa  navicularis,  where  it  changes 

'The  female  urethra,  while  not  so  distinctly  divisible  into  sections,  presents 
essentially  the  same  structure  as  the  male  urethra..  The  epithelium  begins  at  the 
bladder  as  stratified  squamous  of  the  transitional  type,  changes  to  a  two-layered 
stratified  or  pseudostratified,  and  finally  passes  over  into  stratified  squamous  near 
the  urethra]  opening.     Glands  of  Littre'  are  present,  but  are  fewer  than  in  the  male. 


THE  REPRODUCTIVE  SYSTEM. 


287 


to  stratified  squamous.  The  epithelium  rests  upon  a  basement  mem- 
brane, beneath  which  is  a  thin  stroma  rich  in  elastic  fibres  and  hav- 
ing papillae  which  are  especially  prominent  in  the  terminal  dilated 
portion  of  the  urethra,  the  fossa  navicularis.  The  stroma  merges 
without  distinct  demarcation  into  the  submucosa. 

The  submucosa  consists   of  connective  tissue  and,  in  the  penile 
portion,  of  more  or  less  longitudinally  disposed  smooth  muscle.      It 
contains  a  dense  network  of  veins — 
cavernous    veins — which    give    it    the      '   p#  g; 
character  of  erectile  tissue  (Fig.  189).  '  j  %::ff\  -  'v     '"■     ,  :    ^  -. 

The  muscular  coat  is  thickest  in 
the  prostatic  and  membranous  por- 
tions. Here  it  consists  of  a  thin 
inner  longitudinal  and  a  thicker  outer 
circular  layer.  A  definite  muscular 
wall  ceases  at  the  beginning  of  the 
penile  portion,  although  circularly  dis- 


r 


h 


& 


-  d 


Fig.  18S. 


Fig.  189. 


FIG.  188.  — From  Transverse  Section  of  Urethra  and  Corpus  Spongiosum,  including  Mucous 
Membrane  and  part  of  Submucosa.     X  15.    The  dark  spots  represent  the  cavernous  veins. 

FIG.  189.— Vertical  Section  through  Portion  of  Wall  of  Human  Male  Urethra.  X  350.  A,  Mu- 
cous membrane;  B.  submucosa ;  «,  epithelium;  b,  stroma;  c,  cavernous  veins;  cf,  con- 
nective tissue  of  submucosa. 


posed  smooth  muscle  cells  are  found   in  the  outer  part  of  the  sub- 
mucosa of  the  penile  urethra. 

Throughout  the  mucosa  of  the  entire  urethra,  but  most  numerous 
in  the  penile  portion,  are  simple  branched  tubular  mucous  glands, 
the  glands  of  Littre.  They  are  lined  with  columnar  epithelium  and 
the  longer  extend  into  the  submucosa. 


2  88  THE   ORGANS. 

TECHNIC. 

I 1)  For  the  study  of  the  general  topography  of  the  penis,  remove  the  skin  from 
the  organ  and  cut  into  transverse  slices  about  0.5  cm.  in  thickness.  Fix  in  forma- 
lin-Midler's fluid  (technjc  5,  p.  5).  cut  rather  thick  sections  across  the  entire 
penis,  stain  with  haematoxylin-picro-acid-fuchsin  (technic  3.  p.  16)  or  with  haema- 
toxylin-eosin  (technic  1.  p.  16)  and  mount  in  balsam. 

(2)  For  the  study  of  the  structure  of  the  penile  portion  of  the  urethra  and  of 
the  erectile  tissue  of  the  corpus  spongiosum,  cut  away  the  corpora  cavernosa,  leav- 
ing only  the  corpus  spongiosum  and  contained  urethra,  and  treat  as  above.  Sec- 
tions should  be  thin  and  stained  with  haematoxylin-eosin. 

(3)  The  same  technic  is  to  be  used  for  the  membranous  and  prostatic  portions 
of  the  urethra. 

II.    FEMALE    ORGANS. 
The    Ovary. 

The  ovary  is  classed  as  one  of  the  ductless  glands.  Its  specific 
secretion  is  the  ovum.  The  ovary  has  no  duct  system  which  is  di- 
rectly continuous  with  its  structure.  In  place  of  this  it  is  provided 
with  what  may  be  considered  to  be  a  highly  specialized  disconnected 
excretory  duct — the  oviduct  or  Fallopian  tube — which  serves  for  the 
transmission  of  its  secretion  to  the  uterus. 

On  one  side  the  ovary  is  attached  by  a  broad  base,  the  Jiilum,  10 
the  broad  ligament.  Elsewhere  the  surface  of  the  ovary  is  covered 
by  a  modified  peritoneum.  At  the  hilum  the  tissues  of  the  broad 
ligament  pass  into  the  ovary  and  spread  out  there  to  form  the  ovarian 
stroma.  This  consists  of  fibrous  connective  tissue  rich  in  elastic 
fibres  and  containing  many  smooth  muscle  cells.  In  the  deeper 
central  portion  of  the  organ  stroma  alone  is  found.  Here  it  contains 
man)r  large  blood-vessels,  and  constitutes  the  medulla  or  zona  vas- 
culosa  of  the  ovary  (Fig.  190,  2).  From  the  medulla  the  stroma 
radiates  toward  the  surface  of  the  ovary  and  becomes  interspersed 
with  glandular  elements  forming  the  ovarian  cortex  (Fig.  190,  J,  j"'), 
At  the  surface  of  the  ovary,  just  beneath  the  peritoneum,  the  stroma 
forms  a  rather  dense  layer  of  fibrous  tissue,  the  tunica  albuginca.  At 
the  margin  of  the  peritoneal  surface  of  the  ovary  the  connective  tis- 
sue of  the  peritoneum  becomes  continuous  with  the  stroma  of  the 
ovary,  while  the  flat  mesothelium  of  the  general  peritoneum  is  re- 
placed by  a  single  layer  of  cuboidal  cells,  which  covers  the  surface  of 
the  ovary  and  is  known  from  its  function  as  the  germinal  epithelium 
(Fig.  190,  /).  The  parenchyma  or  secreting  portion  of  the  ovary 
consists  of  peculiar  glandular  elements,  the  Graafian  follicles. 


THE  REPRODUCTIVE  SYSTEM. 


289 


The  structure  of  the  Graafian  follicle  can  be  best  appreciated  by 
studying  its  development.      The  follicles  originate  from  the  germinal 


Fig.  i9o.--Semidiagrammatic  Drawing  of  Part  of  Cortex  and  Medulla  of  Cat's  Ovary.  (From 
Schron,  in  Quain's  "Anatomy.")  1,  Germinal  epithelium,  beneath  which  is  3,  the  tunica 
albuginea  ;  2,  medulla,  containing  large  blood-vessels,  4;  2,  2',  fibrous  stroma,  arranged 
around  mature  Graafian  follicle  as  its  theca  folliculi  ;  3',  stroma  of  cortex  ;  5,  small 
(primitive)  Graafian  follicles  near  surface;  6,  same  deeper  in  cortex;  7,  later  stage  of 
Graafian  follicle,  beginning  of  cavity  ;  8  and  8',  still  later  stages  in  development  of  folli- 
cle ;  9,  mature  follicle;  a,  stratum  granulosum  ;  />,  germ  hill;  c.  ovum;  d,  nucleus  (ger- 
minal vesicle)  ;  e,  nucleolus  (germinal  spot). 

epithelium  during  foetal  life.      At  this  time  the  germinal  epithelium 
is   proliferating,  and  certain   of    its    cells    differentiate    into    larger 


Fig.    iqi. — Semidiagrammatic    Drawing  to   show    Development   of     Ovum     from     Germinal 
Epithelium  of  Ovary.     (Duval.  1 

spherical  cells — primitive  ova.      The  primitive  ova  pass  down   into 
the  stroma  accompanied  by  a  considerable  number  of  the  undifferen- 
19 


290 


THE   ORGANS. 


tiated  cells  of  the  germinal  epithelium.  A  cord- like  mass  of  cells  is 
thus  formed,  extending  from  the  surface  into  the  stroma.  These  are 
known  as  Pflfigcr 's  egg  tubes  or  cords  (Fig.  191,  A,  B,  C).  Each 
cord  usually  contains  several  ova.      In  some  cases  the  differentiation 


Fig.  192.— Vertical  Section  through  Cortex  of  Ovary  of  Young  Girl.  X  190.  (Bohm  and  von 
Davidoff.)  a,  Germinal  epithelium;  l\  tunica  albuginea;  c,  follicular  epithelium;  d, 
ovum  ;  e,  primitive  Graafian  follicles  in  ovarian  cortex;  /',  granular  layer  of  large  Graafian 
follicle. 


of  the  ova  cells  does  not  occur  upon  the  surface  but  in  the  cords  after 
they  have  extended  down  from  the  surface.  The  connection  of  the 
cord  with  the  surface  epithelium  is  next  broken  so  that  each  cord 
becomes  completely  surrounded  by  stroma.  It  is  now  known  as  an 
egg  nest.  During  this  process  proliferation  of  the  epithelial  cells  of 
the  cords  and  nests  has  been  going  on,  and  each  ovum  surrounded  by 
a  layer  of  epithelial  cells  becomes  separated  from  its  neighbors  (Fig. 
191,  If).     This  central  ovum  surrounded  by  a  single  layer  of  epithe- 


THE  REPRODUCTIVE  SYSTEM.  291 

lial  cells  (follicular  cells)  is  the  primitive  Graafian  follicle  (Fig.  191, 
D,  Fig.  192,  and  Fig.  193,  a).  The  follicle  increases  in  size,  mainly 
on  account  of  proliferation  of  the  follicular  cells,  which  soon  form 
several  layers  instead  of  a  single  layer,  but  also  partly  on  account  of 
growth  of  the  ovum  itself  (Fig.  193 j.  The  latter  now  leaves  the 
centre  of  the  follicle  and  takes  up  an  eccentric  position.  At  the  same 
time  a  cavity  (or  several  small  cavities  which  later  unite)  appears  near 
the  centre  of  the  follicle  (Fig.  193,  e  and  Fig.  190,  J).  This  is  filled 
with  fluid  which  seems  to  be  in  part  a  secretion  of  the  follicular  cells, 
in  part  a  result  of  their  disintegration.  The  cavity  is  known  as  the 
follicular  cavity  or  antrum,  the  fluid  as  the  liquor  folliculi.  Lining 
the  follicular  cavity  are  several  rows  of  follicular  cells  with  granular 
protoplasm — the  stratum  granulosum.  With  increase  in  the  liquor 
folliculi  the  ovum  becomes  still  further  pressed  to  one  side  of  the 
follicle,  where,  surrounded  by  an  accumulation  of  follicular  cells,  it 
forms  a  distinct  projection  into  the  cavity  (Fig.  194,  and  Fig.  190, 
8  and  p).  This  is  known  as  the  germ  hill  {discus  proligerus — cumu- 
lus obpkorus).     The  cells  of  the  germ  hill  nearest  the  ovum  become 


- 


£T—- 


2 


■■  ..       ■ 


arqej. 


FIG.  193.— From  Section  through  Cortex  of  Ape's  Ovary.  X  150.  (Szymonowicz.)  .?,  Prim- 
itive follicle  ;  b,  ovum,  with  nucleus  and  nucleolus;  c,  zona  pellucida  ;  if,  follicular 
epithelium  ;  e,  follicular  cavity  ;  f,  ovarian  stroma  ;  £\  blood-vessel  in  stroma. 

columnar  and  arranged  in  a  regular  single  layer  around  the  ovum — 
the  corona  radiata  (Fig.  193).  The  ovarian  stroma  immediately  sur- 
rounding the  Graafian  follicle  becomes  somewhat  modified  to  form 
a  sheath  for  the  follicle— the  theca folliculi  (Fig.  194).  This  consists 
of  two   layers,  an  outer  more  dense  fibrous   layer,  the  tunica  fibrosa, 


292  THE   ORGANS. 

and  an  inner  more  cellular  and  vascular,  the  tunica  vasadosa.  Be- 
tween the  thecafolliculi  and  the  stratum  granulosum  is  an  apparently 
structureless  basement  membrane. 

While  these  changes  are  taking  place  in  the  follicle,  the  ovum  is 
also  undergoing  development.  The  ovum  of  the  primitive  follicle  is 
a  spherical  cell,  having  a  diameter  of  from  40  to  70  ;>■  and  the  struc- 
ture of  a  typical  cell.  The  nucleus  or  germinal  vesicle  (so  called  on 
account  of  the  part  it  takes  in  reproduction)  is  about  half  the  diameter 
of  the  cell,  and   is  spherical  and  centrally  placed  (Fig.    193).      It   is 


-g 


,      ,;;c^r^ 


—  e 


■:!> 


d 


FlG.  194.— Section  through  Graafian  Follicle  of  Ape's  Ovary.  X  90.  (Szymonowicz.)  Later 
stage  of  development  than  Fig.  193.  a,  Germ  hill  ;  />,  ovum  with  clear  zona  pellucida, 
germinal  vesicle,  and  germinal  spot;  d,  follicular  epithelium  (membrana  granulosa);  e, 
follicular  cavity  ;  /',  theca  folliculi  ;  g,  blood-vessel. 

surrounded  by  a  double-contoured  nuclear  membrane,  and  contains  a 
distinct  chromatic  network  and  nucleolus  or  germinal  spot.  The 
cytoplasm  is  quite  easily  differentiated  into  a  spongioplasm  network 
and  a  homogeneous  hyaloplasm.  Such  ova  are  present  in  all  active 
ovaries,  i.e.,  during  the  childbearing  period,  but  are  especially  nu- 
merous in  the  ovary  of  the  infant  and  child  (Fig.  192). 

With  the  development  of  the  follicle  the  ovum  increases  in  size 
and  becomes  surrounded  by  a  clear  membrane,  the  zona  pellucida^ 
believed  by  some  to  be  a  cuticular  formation  deposited  by  the  egg 
cell,  by  others  to  be  a  product  of  the  surrounding  follicular  cells. 
Minute  canals  extend  into  the  zona  pellucida  from  its  outer  surface. 
These  contain  processes  of  the  cells  of  the  corona  radiata.      A  narrow 


THE  REPRODUCTIVE  SYSTEM.  293 

cleft,  the  perivitelline  space,  has  been  described  as  separating  the 
ovum  from  the  zona  pellucida.  During  the  growth  of  the  ovum  its 
cytoplasm  becomes  coarsely  granular  from  the  development  of  yolk 
or  deutoplasm  granules.  Immediately  surrounding  the  nucleus,  and 
just  beneath  the  zona  pellucida,  the  egg  protoplasm  is  fairly  free  from 
yolk  granules. 

The  further  maturation  of  the  ovum,  which  is  necessary  before 
the  egg  cell  is  in  condition  to  be  fertilized,  consists  in  changes  in  the 
chromatic  elements  of  the  nucleus,  which  result  in  the  extrusion  of 
the  polar  bodies,  and  apparently  have  as  their  main  object  the  reduc- 
tion in  number  of  chromosomes  to  one-half  the  number  characteristic 
of  the  species.  This  process  has  been  described  (page  42").  In 
many  of  the  lower  animals  maturation  of  the  ovum  is  completed  out- 
side the  ovary.  In  man  and  the  higher  animals  the  entire  process 
takes  place  within  the  ovary,  the  second  polar  body  being  extruded 
just  before  the  escape  of  the  ovum  from  its  follicle. 

The  youngest  of  the  Graafian  follicles  are  found  just  under  the 
tunica  albuginea  near  the  germinal  epithelium,  from  which  they 
originate  (Fig.  190,5).  As  the  follicle  matures  it  passes  deeper  into 
the  cortex.  With  complete  maturity  the  follicle  usually  assumes 
macroscopic  proportions — 8  to  12  mm. — and  often  occupies  the 
entire  thickness  of  the  cortex,  its  theca  at  one  point  touching  the 
tunica  albuginea.  A  thinning  of  the  follicular  wall  nearest  the  sur- 
face of  the  ovary  next  takes  place,  while  at  the  same  time  an  increase 
in  the  liquor  folliculi  determines  increased  intrafollicular  pressure. 
This  results  in  rupture  of  the  Graafian  follicle  and  the  discharge  of 
its  ovum,  together  with  the  liquor  folliculi  and  some  of  the  follicular 
cells. 

An  escape  of  blood  into  the  follicle  from  the  torn  vessels  of  the 
theca  always  accompanies  the  discharge  of  the  ovum.  The  follicle 
again  becomes  a  closed  cavity,  while  the  contained  blood  clot  becomes 
organized  by  the  ingrowth  of  vessels  from  the  theca,  to  form  the  cor- 
pus hcemorrhagicum,  which  represents  the  earliest  stage  in  the  de- 
velopment of  the  corpus  lutcuni. 

The  corpus  luteum  (Fig.  196),  which  replaces  the  corpus  haemor- 
rhagicum,  consists  of  large  yellow  cells — lutein  cells — and  of  connec- 
tive tissue.  The  latter  with  its  blood-vessels  is  derived  from  the 
inner  layer  of  the  theca.  The  origin  of  the  lutein  cells  is  not  clear. 
They  are  described  by  some  as  derived  from  the  connective-tissue 


294 


THE   ORGANS. 


cells  of  the  theca ;  by  others  as  the  result  of  proliferation  of  the  cells 
of  the  stratum  granulosum.  The  cells  have  a  yellow  color  from  the 
presence  of  fatty  (lutein)  granules  in  their  protoplasm,  and  it  is  to 
these  granules  that  the  characteristic  yellow  color  of  the  corpus 
luteum  is  due.  A  definite  cellular  structure  with  a  supporting  con- 
nective-tissue framework  thus  replaces  the  corpus  haemorrhagicum, 


FlG.  195. — Graafian  Follicle  and  Contained  Ovum  of  Cat ;  directly  reproduced  from  a  photo- 
graph of  a  preparation  by  Dahlgren.  X  235.  (From  "The  Cell  in  Development  and  In- 
heritance," Prof.  E.  B.  Wilson;  The  Macmilkm  Company,  publishers.)  The  ovum 
is  seen  lying  in  the  Graafian  follicle  within  the  germ  hill,  the  cells  of  the  latter  imme- 
diately surrounding  the  ovum  forming  the  corona  radiata.  The  clear  zone  within  the 
corona  is  the  zona  pellucida,  within  which  are  the  egg  protoplasm,  nucleus,  and  nucleolus. 
Encircling  the  follicle  is  the  connective  tissue  of  the  theca  folliculi. 


remains  of  which  are  usually  present  in  the  shape  of  orange-colored 
crystals  of  haematoidin.  Hy  degeneration  and  subsequent  absorption 
of  its  tissues  the  corpus  luteum  becomes  gradually  reduced  in  size, 
loses  its  yellow  color,  and  is  then  known  as  the  corpus  albicans. 
This  also  is  mostly  absorbed,  being  finally  represented  merely  by  a 
small  area  of  fibrous  tissue. 

Corpora   lutea  are  divided   into  true  corpora  lutea  (corpora  lutea 
vera  or  corpora   lutea  of  pregnancy)  and  false  corpora   In  tea  (corpora 


THE  REPRODUCTIVE  SYSTEM. 


295 


lutea  spuria).  The  former  replace  follicles  whose  ova  have  under- 
gone fertilization,  the  latter,  follicles  whose  ova  have  not  been  ferti- 
lized. The  structure  of  both  is  similar,  but  the  true  corpus  luteum 
is  larger,  and  both  it  and  its  corpus  albicans  are  slower  in  passing 
through  their  retrogressive  changes,  thus  remaining  much  longer  in 
the  ovary. 

While  the  function  of  the  corpus  luteum  is  not  known,  the  recent 
experiments  of  Fraenkel  seem  to  be  confirmatory  of  the  theory  ad- 
vanced by  Born,  that  the  corpus  luteum  is  a  gland  having  an  internal 
secretion,  which  appears  to  have  some  influence  upon  the  attachment 
of  the  fecundated  ovum  to  the  uterus  and  upon  its  nutrition  during 
the  first  few  weeks  of  its  development.     According  to   Fraenkel  the 


^HP 


it 


b-- 


3 


Fig.  196.— Formation  of  the  Corpus  Luteum  according1  to  Sabotta.  Four  successive  stages 
in  the  mouse.  A,  Vascular  bud  of  tunica  intima  extending  into  the  proliferating  fol- 
licular epithelium.  B,  Vascular  buds  passing  toward  the  central  cavity  ;  between  them  the 
proliferating  follicular  cells,  among  which  leucocytes  have  now  appeared.  C,  Later  stage  ; 
cells  in  distinct  columns  between  strands  of  connective  tissue.  Z>,  Central  cavity  replaced 
by  connective  tissue  resembling  mucous  tissue,  columns  broken  up  by  anastomosis  of  con- 
nective-tissue strands,  it.  Follicular  epithelium  ;  £,  vascular  bud  ;  c.  theca  folliculi  ;  if, 
germinal  epthelium  ;  e,  leucocytes. 


corpus  luteum  is  a  periodically  rejuvenated  ovarian  gland,  which 
gives  to  the  uterus  a  cyclic  nutritional  impulse,  which  prepares  it  for 
the  implantation  of  the  ovum  or  favors  menstruation  whenever  the 
ovum  is  not  fertilized. 


296  THE   ORGANS. 

Of  the  large  number  of  ova— estimated  at  seventy-two  thousand 
— in  the  human  ovaries  only  comparatively  few,  according  to  Henle 
about  four  hundred,  reach  maturity.  The  majority  undergo,  together 
with  their  follicles,  retrogressive  changes  known  as  atresia  of  the 
follicle.  The  nucleus  of  the  ovum,  as  well  as  the  nuclei  of  the  fol- 
licular cells,  passes  through  a  series  of  chromatolytic  changes,  or  in 
some  cases  apparently  simply  atrophies.  The  cell  bodies  undergo 
fatty  or  albuminous  degeneration  and  the  cell  becomes  reduced  to  a 
homogeneous  mass,  which  is  finally  absorbed,  leaving  in  its  place  a 
connective-tissue  scar,  probably  the  remains  of  the  theca  folliculi. 

Blood-vessels. — The  arteries,  branches  of  the  ovarian  and  uterine, 
enter  the  ovary  at  the  hilum  and  ramify  in  the  medulla.  From  these 
are  given  off  branches  which  pass  to  the  cortex  and  end  in  a  capil- 
lary network  in  the  tunica  albuginea.  In  the  outer  layer  of  the 
theca  folliculi  the  capillaries  form  a  wide-meshed  network,  which 
gives  rise  to  a  fine-meshed  network  of  capillaries  in  the  inner  layer 
of  the  theca.  From  the  capillaries  veins  arise  which  form  a  plexus 
in  the  medulla  and  leave  the  ovary  at  the  hilum. 

Lymphatics. — These  begin  as  small  lymph  spaces  in  the  cortex, 
which  communicate  with  more  definite  lymph  vessels  in  the  medulla, 
the  latter  leaving  the  organ  at  the  hilum. 

Nerves. — Medullated  and  non-medullated  fibres  enter  the  ovary 
at  the  hilum  and  follow  the  course  taken  by  the  blood-vessels.  Many 
of  the  fibres  end  in  the  vessel  walls ;  others  form  plexuses  around 
the  follicle  and  end  in  the  theca  folliculi.  Some  describe  fibres  as 
passing  through  the  theca  and  ending  in  the  follicular  epithelium. 
Others  claim  that  nerve  fibres  do  not  enter  the  follicle  proper. 
Groups  of  sympathetic  ganglion  cells  occur  in  the  medulla  near  the 
hilum. 

As  is  the  case  with  the  testicle,  certain  rudimentary  organs,  the 
remains  of  foetal  structures,  are  found  connected  with  the  ovary. 

The  paroophoron  consists  of  a  number  of  cords  or  tubules  of  epi- 
thelial cells,  sometimes  ciliated,  sometimes  non-ciliated.  It  is  found 
in  the  medulla,  or,  more  commonly,  in  the  connective  tissue  of  the 
hilum. 

The  epoophoron  is  a  similar  structure  found  in  the  folds  of  the 
broad  ligament.  Its  tubules  open  into  a  duct  known  as  Gartner's 
duct.      In  man  this  duct  ends  blindly.      In  some  of  the  lower  animals 


THE  REPRODUCTIVE  SYSTEM. 


297 


it  opens  into  the  vagina.  Both  paroophoron  and  epoophoron  are 
remains  of  the  embryonal  mesonephros,  the  former  of  its  posterior 
segment,  the  latter  of  its  middle  segment. 

The  Oviduct. 

The  oviduct  or  Fallopian  tube  is  the  excretory  duct  of  the  ovary, 
serving  for  the  transmission  of  the  discharged  ovum  from  ovary  to 
uterus.  Although  there  is  no  sharp  demarcation  between  them,  it  is 
convenient  to  divide  the  tube  into  three  segments:  (1)  The  isthmus, 
beginning  at  the  uterus  and  extending  about  one-third  the  length  of 


FIG.  197.— Cross  Section  of  Oviduct  near  Uterine  End.     a,  Mucous  membrane  ;  i,  circular  mus- 
cle coat ;  c,  longitudinal  muscle  coat ;  d,  connective  tissue  of  serous  coat.     (Orthmann.) 

the  tube ;  (2)  the  ampulla,  about  twice  the  diameter  of  the  isthmus, 
and  occupying  somewhat  more  than  the  middle  third ;  and  (3)  the 
fimbriated  or  ovarian  extremity. 

The  walls  of  the  oviduct  consist  of  three  coats:  (1)  Mucous,  (2) 
muscular,  and  (3)  serous  (Figs.  197  and  198). 

The  mucous  membrane  presents  numerous  longitudinal  foldings. 
In  the  embryo  four  of  these  folds  can  usually  be  distinguished,  and 
these  are  known  as  primary  folds.  In  the  adult  many  secondary- 
folds  have  developed  upon  the  primary,  especially  in  the  ampulla  and 
fimbriated  extremity  where  the  folds  are  high  and  complicated  (Fig. 
198).     The  epithelium  lining  the  tube  is  of  the  simple   columnar 


298  THE   ORGANS. 

ciliated  type,  and  completely  covers  the  foldings  of  the  mucous  mem- 
brane. The  ciliary  motion  is  toward  the  uterus.  The  stroma  con- 
sists of  a  cellular  connective  tissue,  quite  compact  in  structure  in  the 
isthmus,  where  the  folds  are  low,  more  loosely  arranged  in  the  high 
folds  of  the  ampulla  and  fimbriated  extremity. 

The  muscular  coat  consists   of   an   inner   circular  and  an  outer 
longitudinal  layer.     The  latter  is  a  comparatively  thin  layer  in  the 


Ife**, 


m 

M 


FIG.  198.— Cross  Section  of  Oviduct   near  Fimbriated    Extremity,  showing   complicated   fold- 
ings of  mucous  membrane.      (Orthmann.) 

isthmus,  consists  of  discontinuous  groups  of  muscle  cells  in  the  am- 
pulla, and  in  the  fimbriated  extremity  is  frequently  absent. 

The  serous  coat  has  the  usual  structure  of  peritoneum. 

The  larger  blood-vessels  run  in  the  stroma  along  the  bases  of  the 
folds.  They  send  off  branches  which  give  rise  to  a  dense  capillary 
network  in  the  stroma. 

Of  the  lymphatics  of  the  tube  little  is  known. 

The  nerves  form  a  rich  plexus  in  the  stroma,  from  which  branches 
pass  to  the  blood-vessels  and  muscular  tissue  of  the  walls  of  the  tube 
and  internally  as  far  as  the  epithelial  lining. 

TECHNIC. 

(1)  Child's  Ovary.  — Remove  the  ovary  of  a  new-born  child,  being  careful  not 
to  touch  the  surface  epithelium,  fix  in  Zenker's  fluid  (technic  9,  ]»•  c>)<  and  harden 
in  alcohol.  Cut  sections  of  the  entire  organ  through  the  hilum.  Stain  with 
haematoxylin  eosin  (technic  1.  p.  16)  and  mount  in  balsam. 


THE  REPRODUCTIVE  SYSTEM.  299 

(2)  For  the  purpose  of  studying  the  Graafian  follicle  in  the  different  stages  of 
its  development  remove  an  ovary  from  an  adult  cat  or  dog  and  treat  as  above. 
Technic  (1).  These  sections  also  as  a  rule  are  satisfactory  for  the  study  of  the  cor- 
pus luteum. 

(3)  The  human  adult  ovary  is  little  used  for  histological  purposes  on  account 
of  the  few  follicles  it  usually  contains  and  its  proneness  to  pathological  changes. 
Its  study  is,  however,  so  extremely  important,  especially  with  reference  to  the 
pathology  of  the  ovary,  that  if  possible  a  normal  human  ovary  should  be  obtained 
from  a  young  subject  for  purposes  of  comparison  with  the  above.  Technic 
same  (1). 

(4)  For  studying  the  egg  tubes  of  Pfliiger  and  their  relation  to  the  germ  epi- 
thelium, ovaries  of  the  human  foetus,  and  of  very  young  cats,  dogs,  and  rabbits  are 
satisfactory.     Technic  (1). 

(5)  Sections  of  the  fimbriated  end  of  the  oviduct  are  usually  found  in  the  sec- 
tions of  ovary.  For  the  study  of  other  parts  of  the  tube,  cut  out  thin  pieces  from 
different  regions,  fix  in  formalin-M tiller's  fluid,  stain  transverse  sections  with  has- 
matoxylin-eosin,  and  mount  in  balsam. 

The  Uterus. 

The  wall  of  the  uterus  consists  of  three  coats  which  from  without 
inward  are  serous,  muscular,  and  mucous. 

The  serous  coat  is  a  reflection  of  the  peritoneum,  and  has  the  usual 
structure  of  a  serous  membrane. 

The  muscu/an's  consists  of  bundles  of  smooth  muscle  cells  sepa- 
rated by  connective  tissue.  The  muscle  has  a  general  arrangement 
into  three  layers,  an  inner,  a  middle,  and  an  outer,  which  are  distinct 
in  the  cervix,  but  not  well  defined  in  the  body  and  fundus. 

The  inner  layer — stratum  submucosum — is  mainly  longitudinal, 
although  some  obliquely  running  bundles  are  usually  present. 

The  middle  layer — called  from  the  large  venous  channels  which 
it  contains,  the  stratum  vasculare — is  the  thickest  of  the  three  layers 
forming  the  main  bulk  of  the  muscular  wall.  It  consists  mainly  of 
circularly  disposed  muscle  bundles. 

The  outer  layer — stratum  supravasculare — is  thin  and  consists 
partly  of  circular  bundles,  partly  of  longitudinal.  The  latter  pre- 
dominate and  form  a  fairly  distinct  layer  just  beneath  the  serosa. 

The  muscle  cells  of  the  uterus  are  long  spindle-shaped  elements, 
some  having  pointed,  others  blunt,  branched,  or  frayed  ends.  In  the 
virgin  uterus  they  have  a  length  of  from  40  to  60 , a. 

During  pregnancy  the  muscular  tissue  of  the  uterus  is  greatly 
increased.  This  is  clue  partly  to  increase  in  the  number,  partly  to 
increase  in  the  size  of  the  muscle  cells.  At  term  the  muscle  cells 
frequently  have  a  length  of  from  250  to  600,". 


;oo 


THE   ORGANS. 


The  mucous  membrane.  As  the  mucosa  presents  marked  varia- 
tion in  structure,  dependent  upon  the  functional  condition  of  the 
organ,  it  is  necessary  to  describe  : 

i.   The  mucosa  of  the  resting  uterus. 

2.  The  mucosa  of  the  menstruating  uterus. 

3.  The  mucosa  of  the  pregnant  uterus. 


wt 


tOlr.S. 


i.  The  Mucosa  of  the  Resting  Uterus. 

This  is  from  1  to  2  mm.  thick,  and  consists  of  a  stroma,  glands, 
and  a  lining  epithelium  (Fig.  199).  The  stroma  resembles  embryonal 
connective  tissue,  consisting  of  fine  fibrils  and  long,  irregular  branch- 
ing cells  which  form  a  sort 
b  of  network,  the  meshes  of 
which  are  filled  in  with  lym- 
phoid cells  and  leucocytes. 
The  epithelium  is  '  of  the 
c  simple  high  columnar  ciliated 
variety,  the  ciliary  motion 
being  toward  the  cervix.  A 
basement  membrane  separates 
the  epithelium  from  the  under- 
lying stroma.  The  glands  are 
simple  forked  tubules  lined  by 
a  single  layer  of  columnar 
ciliated  cells  resting  upon  a 
basement  membrane  and  con- 
tinuous with  the  surface  cells. 
The  glands  extend  completely 
through  the  stroma.  Near  the 
surface  they  run  a  compara- 
tively straight  course.  Deeper 
in  the  stroma  their  course  is 
more  tortuous,  while  the  fundus  is  frequently  turned  at  right  angles 
to  the  rest  of  the  tubule. 

In  the  cervix  the  stroma  is  firmer  and  less  cellular,  and  the  rau- 
cous membrane  is  thicker  and  presents  numerous  folds — the  plicce 
palmalce.  The  epithelium  is  higher  than  in  the  body  of  the  organ. 
In  addition  to  glands  like  those  found   in  the  body  of  the  uterus,  the 


Pi 


Prom  Uterusof  Young  Woman.  (From 
Hohm  and  von  Davidoff;  preparation  by  Dr. 
J.  Amann.)  X  34.  a.  Mucous  membrane ;  J, 
surface  epithelium  ;  c,  gland  ;  e,  muscle. 


THE  REPRODUCTIVE  SYSTEM.  301 

cervical  mucosa  contains  peculiar  short,  sac-like  invaginations  lined 
with    a  continuation    of    the  surface    epithelium,    which    secrete  a 
glairy  mucus.      Closure  of    the 
mouths  of  some  of  these  sacs  fre- 
quently occurs,    leading  to  the  .     ..  ": -^\ 
formation     of    retention    cysts, 
the  so-called  ovula  Nabothi.    At  fa 

about    the   junction    of    middle    a  ..    ■-■ .—     •         ..:... .--■ 

and  lower  thirds  of  the  cervical    /,         .......  -i  ^r-:;^ d 

canal  a  change   takes  place   in  ..:   '    \ 

the     epithelium.         Here     the    e  '"  \X'  //  " '"•  - 

simple    columnar    ciliated    epi-  ...  >r         '    '^ — ---.:' 

*'"'  .  -^  ■--. 

thelium    of    the    upper  part  of    f~  """"---// 

the  cervix  gradually  passes  over 

m  Fig.  200. — From  Section   of   Dog's   Cervix.     X  4. 

into    a    Stratified    Squamous    epi-        (Technics' 2,  p.  310.)    «,  Cervical   canal;  b,  mu- 

thelium.     Near   the  external  os     cosa '  c\  folds  °/  mucosa  W™**}™^  * 

muscle  la\-ers  of  cervix;  e,  epithelium  of   va- 
papilla?    appear,   the  vaginal   SUr-        ginaand  vaginal  surface  of  cervix;/,  vaginal 
.  .  epithelium  ;  g,  vaginal  mucosa ;  //,  submucosa 

face  Of  the  CerVIX  being  COVered        and  muscularis  of  vagina  ;  /,  blood-vessels. 

with  a  stratified  squamous  epi- 
thelium with  underlying  papillae  similar  to  and  continuous  with  that 
of  the  vagina. 

Near  the  external  os  the  epithelium  changes  over  into  the  strati- 
fied squamous  epithelium  with  underlying  papillae,  similar  to  that  of 
the  external  surface  of  the  cervix. 

2.  The  Mucosa  of  the  Menstruating  Uterus. 

This  consists  of  the  same  structural  elements  as  the  mucosa  of 
the  resting  uterus  :  stroma,  glands,  and  lining  epithelium.  These, 
however,  undergo  certain  changes  which  maybe  conveniently  divided 
into  three  stages  : 

(a)  The  stage  of  preparation. 

(/>)   The  stage  of  menstruation  proper. 

(c)  The  stage  of  reparation. 

(a)  The  Stage  of  Preparation. — This  begins  several  days 
before  the  actual  flow  of  blood,  and  is  marked  by  an  intense  hyperae- 
mia  determining  a  swelling  and  growth  of  the  entire  mucosa.  The 
blood-vessels,  especially  the  capillaries  and  veins,  become  greatly 
distended,  thus  contributing  largely  to  the  increase  in  thickness  of 
the  mucosa.      There  are  also  proliferation  of  the  connective-tissue 


;o2 


THE   ORGAXS. 


lllllll; 


cells,  an  increase  in  the  number  of  leucocytes,  and  a  growth  of  the 
uterine  glands.  The  surface  at  the  same  time  becomes  irregular,  the 
glands  opening  into  deep  pits  or  depressions,  and  the  glands  them- 
selves become  more  tortuous  and   their  lumina  more  widely  open. 

The  mucous  membrane  has  now 
reached  a  thickness  of  about 
6  mm.,  and  is  known  as  the 
decidua  menstrualis  (Fig.  201). 
(&)  The  Stage  of  Men- 
struation Proper. — This  is 
marked  by  the  escape  of  blood 
from  the  engorged  vessels  and 
the  appearance  of  the  external 
phenomena  of  menstruation. 
The  blood  escapes  partly  by 
rupture  of  the  vessel  walls, 
partly  by  diapedesis.  The  hem- 
orrhage is  at  first  subepithelial, 
but  the  epithelium  soon  gives 
way  and  the  blood  escapes  into 
the  cavity  of  the  uterus.  Much 
difference  of  opinion  exists  as 
to  the  amount  of  epithelial  de- 
struction during  menstruation, 
some  claiming  that  the  entire 
epithelium  is  destroyed  with  each 
menstrual  period,  others  that  the 
epithelium  remains  almost  in- 
tact. Complete  destruction  of 
the  epithelium  is  hardly  compatible  with  the  restoration  of  the  epithe- 
lium which  always  follows  menstruation.  While  there  is  undoubtedly 
destruction  of  most  or  all  of  the  surface  epithelium  and  of  the  glands 
to  some  considerable  depth,  the  deeper  portions  of  the  glands  always 
remain  to  take  part  in  the  succeeding  regenerative  phenomena. 

(c)  The  Stage  of  Reparation. — After  from  three  to  five  days 
the  bleeding  from  the  uterine  mucosa  ceases  and  the  return  to  the 
resting  condition  begins.  This  is  marked  by  disappearance  of  the 
congestion,  by  decrease  in  thickness  of  the  mucosa  and  in  the  size  of 
the  glands,  and  by  restoration  of  the  surface  epithelium. 


U~i^(iWf-;''<ri--^f $l-'-$'^'' ■  0  ':' 


Fig.  201.— Section  through  Mucous  Membrane 
of  Virgin  Uterus  during  First  Day  of  Men- 
struation. X  30.  (Schaper.)  <r,  Surface  of 
epithelium  ;  b,  disintegrating  surface  ;  c,  pit- 
like depression  in  mucous  membrane ;  d, 
excretory  duct;  e,  blood-vesseis  ;  g;  gland 
tubule;  //,  dilated  gland  tubule;  w,  muscu- 
laris. 


THE  REPRODUCTIVE  SYSTEM.  3°3 

3.  The  Mucosa  of  the  Pregnant  Uterus. 

This  is  known  as  the  decidua  graviditatis ,  and  presents  changes 
in  structure  somewhat  similar  to  those  which  occur  during  menstrua- 
tion, but  more  extensive.      It  is  divided  into  three  parts  : 

id)  The  decidua  serotina  or  decidua  basalis — that  part  of  the 
mucosa  to  which  the  ovum  is  attached. 

(p)  The  decidua  refiexa  or  decidua  capsularis — that  part  of  the 
mucosa  which  surrounds  the  ovum. 

(c)  The  decidua  vera — -which  consists  of  all  the  remaining  mucosa. 

The  development  of  the  decidua  vera  resembles  the  changes  which 
take  place  in  the  mucosa  during  menstruation.  There  is  the  same 
thickening  of  the  mucosa,  and  this  thickening  is  due  to  the  same 
factors,  i.e.,  distention  of  the  blood-vessels  and  proliferation  of  the 
tissue  elements.  These  changes  are,  however,  much  more  extensive 
than  during  menstruation.  The  superficial  part  of  the  stroma  be- 
tween the  mouths  of  the  glands  becomes  quite  dense  and  firm,  form- 
ing the  compact  layer.  The  deeper  part  of  the  stroma  contains  nu- 
merous cavities,  which  are  the  lumina  of  the  now  widely  distended  and 
tortuous  glands.      This  is  known  as  the  spongy  layer. 

Within  the  stroma,  especially  of  the  compact  layer,  develop  the 
so-called  decidual  cells.  These  are  peculiar  typical  cells  derived  from 
connective  tissue.  They  are  of  large  size  (30  to  100/;),  vary  greatly 
in  shape,  and  in  the  later  months  of  pregnancy  have  a  rather  charac- 
teristic brown  color,  which  they  impart  to  the  superficial  layer  of  the 
decidua  vera.  They  are  mostly  mononuclear,  although  polynuclear 
forms  occur. 

During  the  latter  half  of  pregnancy  there  is  a  gradual  thinning 
of  the  decidua  vera,  due  apparently  to  pressure.  The  necks  of  the 
glands  in  the  compact  layer  disappear,  and  the  gland  lumina  in  the 
spongy  layer  are  changed  into  elongated  spaces,  which  lie  parallel  to 
the  muscular  layer. 

The  decidua  refiexa  and  decidua  serotina  have  at  first  the  same 
structure  as  the  decidua  vera.  The  decidua  refiexa  undergoes  hyaline 
degeneration  during  the  early  part  of  pregnancy,  and  by  the  end  of 
gestation  has  either  completely  disappeared  (Minot)  or  has  fused  with 
the  decidua  vera  (Leopold). 

The  decidua  serotina  undergoes  changes  connected  with  the 
development  of  the  placenta. 


304 


THE  ORGANS. 


The  Placenta.' 

The  placenta  consists  of  two  parts,  one  of  which  is  of  maternal 
origin — placenta  uterina — the  other  of  foetal  origin — the  placenta  fee '- 
talis.  As  it  is  in  the  placenta  that  the  interchange  takes  place 
between  the  maternal  and  the  foetal  blood,  the  relations  between  the 
maternal  and  foetal  parts  of  the  placenta  are  extremely  intimate. 
This  relation  consists  essentially  in  the  growing  out  from  the  foetal 
placenta  of  finger-like  projections — villi — which  penetrate  the  mater- 
nal placenta,  the  latter  being  especially  modified  for  their  reception. 

The  Placenta  Fcetalis.  — This  is  a  differentiated  portion  of  the 
chorion.  On  the  surface  directed  toward  the  foetus  the  chorion  after 
the  third  month  is  covered  by  a  delicate  foetal  membrane,  the  placen- 
tal portion  of  the  amnion.      This  consists  of  a  surface  epithelium, 


Fig.  202. — Diagram  of  Human  Placenta  at  Close  of  Pregnancy.  (Schaper.)  a,  Amnion ;  b, 
chorion  ;  c,  chorionic  villi ;  d,  intervillous  spaces  ;  e,  floating  villus;  f,  fastening  villi ;  ft, 
spiral  artery  ;  v,  vein  ;  A,  compact  layer,  />',  cavernous  layer  of  clecidua  serotina  ;  C, 
muscular  is. 

resting  upon  a  layer  of  embryonal  connective  tissue  which  attaches 
it  to  the  chorion.  The  chorion  consists  of  (a)  a  compact  layer — the 
membrana  chorii — composed  at  first  of  embryonal,  later  of  fibrous, 
connective  tissue,  and  containing  the  main  branches  of  the  umbilical 

I  01  E  igs.  202  and  203,  also  for  many  facts  as  t<>  die  structure  of  the  placenta, 
the  writer  is  indebted  to  the  excellent  chapter  on  the  subject  added  by  Prof,  Alfred 
Si  haper  to  the  fifth  edition  of  StShr's  "  Textbook  of  1 1  istology." 


THE  REPRODUCTIVE  SYSTEM. 


305 


vessels  and  an  inner  villous  layer,  which  gives  rise  to  finger-like 
projections  which  extend  down  from  the  foetal  into  the  maternal  pla- 
centa and  serve  to  connect  the  two. 

The  chorionic  villi  first  appear  as  short  projections  composed 
entirely  of  epithelium.  Each  of  these  primary  villi  branches  di- 
chotomously,  giving  rise  to  a  num- 
ber of  secondary  villi.  As  they 
develop,  the  central  portion  of  the 
original  solid  epithelial  structure  is 
replaced  by  connective  tissue.  Septa 
of  connective  tissue  from  the  ma- 
ternal placenta  pass  down  among 
the    villi    and    separate    them    into  MMT^i 

groups  or  cotyledons.  The  main  or 
primary  villi  run  a  quite  straight 
course  from  the  chorion  into  the 
maternal  placental  tissue,  appar- 
ently serving  to  secure  firm  union 
between  the  two.  They  are  thus 
known  as  roots  of  attachment  or 
fastening  villi  (Fig.  202,/).  The 
secondary  villi  are  given  off  later- 
ally from  the  primary  villi,  end 
freely  in  the  spaces  between  the 
latter — intervillous  spaces  (Fig.  202,  d) 
floating  villi  (Fig.  202,  e). 

The  chorionic  villus  thus  consists  of  a  central  core  of  connective 
tissue  covered  by  a  layer  of  epithelium.  The  connective  tissue  is  of 
the  mucous  type  and  serves  for  the  transmission  of  numerous  blood- 
vessels. In  the  villi  of  early  pregnancy  the  epithelium  consists  of 
an  inner  layer  of  distinctly  outlined  cells  and  an  outer  layer  of  fused 
cell  bodies — a  syncytium  (Fig.  203,  A,  a) — containing  small  scattered 
nuclei.  The  villi  of  the  later  months  of  pregnancy  have  no  definite 
epithelial  covering,  but  are  surrounded  by  a  delicate  homogeneous 
membrane,  probably  the  remains  of  the  syncytium.  At  various 
points  on  the  surface  of  the  villus  are  groups  of  nuclei.  These  stain 
intensely,  are  surrounded  by  a  homogeneous  protoplasm,  and  form 
knob-like  projections  above  the  general  surface  of  the  villus.  They 
are  known  as  cell  patches,  or  more  properly  as  unclear  groups  (Fig. 


Fig.  203. — Cross  Sections  of  Human  Chori- 
onic Villi  at  End  of  Pregnancy.  X  250. 
(Schaper.)  .4,  Small  villus;  B,  larger 
villus,  a.  Protoplasmic  coat  (syncytium); 
b,  epithelial  nucleus  ;  c,  nuclear  groups  ; 
d,  small  artery  ;  e,  small  vein  ;  f,  capil- 
laries" 


-and  are  known  as  free  or 


306  THE   ORGANS. 

203,  c),  and  represent  remains  of  the  nuclei  of  the  epithelium  of  the 
younger  villus.  Between  the  nuclear  groups  the  villus  is  covered 
only  by  a  thin  homogeneous  membrane.  Small  villi  usually  resem- 
ble more  closely  in  structure  the  younger  villus,  being  frequently 
covered  by  a  nucleated  syncytium.  Portions  of  the  syncytium,  espe- 
cially of  older  villi,  sometimes  become  changed  into  a  peculiar  hya- 
line substance  containing  numerous  channels.  This  is  known  as 
canalized  fibrin,  and  may  form  dense  layers  upon  the  surface  of  the 
chorion. 

The  Placenta  Uterina. — This  develops  from  the  decidua  sero- 
tina.  The  latter  becomes  much  thinner  than  the  rest  of  the  decidua 
(decidua  vera),  but  still  shows  a  division  into  a  deeper  spongy  portion 
containing  gland  tubules,  and  a  superficial  compact  portion  in  which 
are  large  numbers  of  decidual  cells.  From  the  superficial  portion 
connective-tissue  septa — placental  septa — grow  into  the  fcetal  pla- 
centa, as  described  above,  separating  its  villi  into  cotyledons.  Near 
the  margins  of  the  placenta  these  septa  pass  to  the  chorionic  mem- 
brane and  form  beneath  it  a  thin  membrane,  the  snbcliorionic  placental 
decidua.  At  the  edge  of  the  placenta,  where  decidua  serotina  passes 
over  into  the  thicker  decidua  vera,  there  is  a  close  attachment  of  the 
chorion  to  the  former. 

As  the  placenta  serves  as  the  place  of  interchange  of  materials  be- 
tween the  maternal  and  the  fcetal  circulations,  the  arrangement  of  the 
placental  blood-vessels  is  of  especial  importance.  Arterial  branches 
from  vessels  of  the  uterine  muscularis  enter  the  serotina.  In  the 
very  tortuous  course  which  these  vessels  take  through  the  serotina 
(Fig.  202, g)  their  walls  lose  their  muscular  and  connective-tissue  ele- 
ments and  become  reduced  to  epithelial  tubes.  These  branch  in  the 
placental  septa  and  finally  open  into  the  intervillous  spaces  along  the 
edges  of  the  cotyledons.  The  veins  take  origin  from  these  spaces 
near  the  centres  of  the  cotyledons.  The  maternal  blood  thus  passes 
through  the  intervillous  spaces  from  periphery  to  centre,  and  in  its 
course  comes  into  direct  contact  with  the  freely  terminating  chorionic 
villi.  It  is  to  be  noted  that  the  blood-vessel  systems  of  the  mother 
and  of  the  foetus  are  both  closed  systems,  and  that  consequently  there 
is  no  direct  admixture  of  maternal  and  fcetal  blood.  Interchange  of 
materials  must  therefore  always  take  place  through  the  capillary  walls 
and  through  the  walls  of  the  chorionic  villi. 

Blood-vessels. — The  arteries  enter  the  uterus  from  the  broad  liga- 


THE  REPRODUCTIVE  SYSTEM.  307 

raent  and  pass  to  the  stratum  vasculare  of  the  muscularis,  where  they 
undergo  extensive  ramification.  From  the  arteries  of  the  stratum 
vasculare  branches  pass  to  the  mucosa  and  give  rise  to  capillary  net- 
works, which  surround  the  glands  and  are  especially  dense  just  be- 
neath the  surface  epithelium.  From  these  capillaries  the  blood 
passes  into  a  plexus  of  veins  in  the  deeper  portion  of  the  mucosa,  and 
these  in  turn  empty  into  the  venous  plexuses  of  the  stratum  vascu- 
lare. Thence  the  veins  accompany  the  arteries,  leaving  the  uterus 
through  the  broad  ligament. 

Lymphatics. — These  begin  as  minute  spaces  in  the  stroma  and 
empty  into  the  more  definite  lymph  channels  of  the  muscularis,  which 
are  especially  well  developed  in  the  stratum  vasculare.  These  in 
turn  communicate  with  the  larger  lymph  vessels  in  the  subserous 
connective  tissue. 

Nerves. — Both  medullated  and  non-medullated  nerve  fibres  occur 
in  the  uterus.  The  latter  are  associated  with  minute  sympathetic 
ganglia  and  supply  the  muscular  tissue.  The  medullated  fibres  form 
plexuses  in  the  mucosa,  from  which  are  given  off  fine  fibres  which 
terminate  freely  between  the  cells  of  the  surface  epithelium  and  of 
the  uterine  glands. 

The  Vagina. 

The  wall  of  the  vagina  consists  of  four  coats,  which  from  without 
inward  are  fibrous,  muscular,  submucous,  and  mucous. 

The  fibrous  coat  consists  of  dense  connective  tissue  with  many 
coarse  elastic  fibres.  It  serves  to  connect  the  vagina  with  the  sur- 
rounding structures. 

The  muscular  coat  is  indistinctly  divided  into  an  outer  longitu- 
dinal and  an  inner  circular  layer.  The  latter  is  usually  not  well 
developed  and  may  be  absent. 

The  submucosa  is  a  layer  of  loose  connective  tissue,  especially 
rich  in  elastic  fibres  and  blood-vessels.  Numerous  large  venous 
channels  give  to  the  submucosa  the  character  of  erectile  tissue. 

The  mucous  membrane  consists  of  a  papillated  connective-tissue 
stroma  of  mixed  fibrous  and  elastic  tissue.  The  stroma  usually  con- 
tains diffuse  lymphoid  tissue  and  more  rarely  solitary  nodules. 
Covering  the  stroma  is  a  stratified  squamous  epithelium,  the  surface 
cells  of  which  are  extremely  thin.  The  surface  of  the  mucosa  is  not 
smooth,  but  is  folded  transversely,  forming  the  so-called  rugce.      Most 


3°S  THE   ORGANS. 

authorities  agree  that  glands  are  wanting  in  the  vagina,  the  mucus 
found  there  being  derived  from  the  glands  of  the  cervix. 

Blood-vessels. — The  larger  blood-vessels  run  in  the  submucosa, 
giving  off  branches  which  break  up  into  capillary  networks  in  the 
submucosa,  muscularis,  and  stroma.  The  vascular  networks  have  a 
genera]  direction  parallel  to  the  surface.  The  capillaries  empty  into 
veins  which  form  a  plexus  of  broad  venous  channels  in  the  muscu- 
laris. 

The  Lymphatics. — These  follow  in  general  the  distribution  of  the 
blood-vessels. 

Nerves. — Nerve  fibres  from  both  cerebro-spinal  and  sympathetic 
systems  are  found  in  the  vagina.  Medullated  (sensory)  fibres,  the 
dendrites  of  spinal  ganglion  cells,  form  plexuses  in  the  mucosa,  from 
which  are  given  off  delicate  non-medullated  terminals  to  the  epithe- 
lial cells.  Non-medullated  sympathetic  fibres  supply  the  muscularis 
and  the  muscle  of  the  vessel  walls.  Along  these  nerves  are  small 
sympathetic  ganglia. 

In  the  vestibule  the  epithelium  gradually  takes  on  the  structure 
of  epidermis.  Here  are  located  small  mucous  glands — glandultc 
vestibulares  minores — especially  numerous  around  the  clitoris  and 
opening  of  the  urethra.  Larger  mucous  glands — glandules  vestibu- 
lares ma/ores,  or  glands  of  Bartholin — analogous  to  Cowper's  glands 
in  the  male,  are  also  found  in  the  walls  of  the  vestibule. 

The  clitoris  consists  mainly  of  erectile  tissue  similar  to  that  of 
the  corpora  cavernosa  of  the  penis.  It  is  covered  with  a  thin  epithe- 
lium with  underlying  papillae,  and  is  richly  supplied  with  nerves  hav- 
ing highly  specialized  terminations. 

Development  of  the  Urinary  and  Reproductive  Systems. 

The  urinary  organs  are  peculiar  in  that  three  consecutive  organs 
arc  concerned  in  their  development,  although  only  the  last  of  these 
actually  gives  rise  to  functionating  adult  organs,  the  other  two  being 
represented  in  the  adult  only  by  rudimentary  structures.  These 
three  organs,  in  the  order  of  their  appearance,  are  the  pronephros, 
the  mesonephros,  and  the  metanephros.  All  of  these  bodies  develop 
from  the  mesoderm,  first  appearing  as  symmetrically  placed  ridges, 
which  project  into  the  primitive  body  cavity  as  the  Wolffian  ridges. 


THE  REPRODUCTIVE  SYSTEM.  309 

The  pronephritic  or  Wolffian  ducts  and  the  pronephros  are  the 
earliest  of  the  urinary  structures  to  appear.  The  former  consist  at 
first  of  solid,  elongated  groups  of  cells,  situated  in  the  Wolffian  ridge. 
These  later  acquire  lumina  and  become  tubules. 

The  pronephros  consists  of  two  evaginations  of  the  epithelium  of 
the  primitive  body  cavity  into  the  tissues  of  the  Wolffian  ridges,  near 
the  anterior  end  of  the  Wolffian  duct.  Only  one  of  these  develops 
into  tubules,  and  both  disappear  early  in  embryonic  life.  In  the 
female  the  Wolffian  duct  degenerates ;  in  the  male  it  remains  to 
form  the  vas  deferens  and  tail  of  the  epididymis. 

When  the  human  embryo  has  reached  a  length  of  from  3  to 
4  mm.,  a  number  of  cords  of  cells,  the  origin  of  which  is  still 
doubtful,  appear  in  the  Wolffian  ridge.  These  acquire  lumina, 
which  at  one  end  communicate  with  the  Wolffian  duct,  while  at  the 
other  glomeruli  develop,  which  contain  blood-vessels  derived  from  the 
aorta.  This  development  of  tubules  and  glomeruli  results  in  a  large 
increase  in  the  size  of  the  Wolffian  ridges,  which  are  now  known  as 
the  Wolffian  bodies  or  mesonephros.  The  latter  reach  their  greatest 
development  between  the  sixth  and  eighth  embryonic  week,  after 
which  the  tubules  and  glomeruli  undergo  retrogressive  changes.  In 
the  male  the  anterior  tubules  remain  to  form  the  head  of  the  epidid- 
ymis, while  the  posterior  tubules  are  represented  only  by  the  rudimen- 
tary paradidymis  or  organ  of  Giraldes.  In  the  female  the  Wolffian 
body  remains  only  as  two  rudimentary  structures — the  parovarium 
and  the  paroophoron. 

During  the  retrogressive  changes  in  the  mesonephros  a  new 
tubular  structure  appears  as  an  outgrowth  from  the  dorsum  of  the 
Wolffian  duct.  This  tubule  is  known  as  the  metanephros,  and  from 
it  are  developed  the  ureter  and  kidney.  The  end  of  the  tubule  at 
which  the  kidney  is  to  develop  next  divides  into  a  number  of  branches, 
which  end  iu  expansions,  the  primary  renal  vesicles.  From  the  lat- 
ter the  uriniferous  tubules  develop.  During  the  development  of 
these  tubules  septa  grow  in  from  the  capsule,  which  now  surrounds 
the  primitive  kidney  in  such  a  manner  as  to  separate  the  groups  of 
tubules  which  develop  from  each  primary  vesicle.  In  this  way  the 
kidney  becomes  lobulated,  the  lobulation,  however,  disappearing  after 
birth.  The  renal  corpuscles  or  Malpighian  bodies  are  formed,  as 
already  described  (page  258),  by  invaginations  of  the  developing 
tubules  by  branches  of  the  renal  artery. 


3iO  THE   ORGANS. 

At  about  the  height  of  development  of  the  Wolffian  body  there 
appears  along  the  inner  side  of  each  Wolffian  ridge  a  thickening 
of  the  mesodermic  cells,  which  thus  form  a  distinct  projection,  the 
genital  ridge.  This  is  the  earliest  trace  of  a  sexual  gland,  and  is  at 
first  identical  in  the  two  sexes.  By  differentiation  of  these  meso- 
dermic cells  are  formed,  according  to  sex,  the  ovaries  or  testes. 

Into  the  genital  ridge  there  extends  an  invagination  of  the  peri- 
toneum to  form  the  Mullerian  duct.  In  the  male  this  degenerates, 
its  anterior  part  being  represented  in  the  adult  by  the  stalked  hy- 
datid or  hydatid  of  Morgagni,  its  posterior  part  by  the  uterus  mascu- 
linus.  In  the  female  the  Mullerian  ducts  unite  below  to  form  the 
uterus,  while  above  they  remain  separate,  forming  the  Fallopian 
tubes. 

TECHNIC. 

(i)  A  human  uterus — if  possible  from  a  young  adult — or,  if  this  cannot  be  ob- 
tained, the  uterus  of  a  cat  or  dog,  is  cut  transversely  into  slices  about  i  cm.  thick 
and  fixed  in  Zenker's  fluid  (technic  9,  p.  6)  or  in  formalin-Midler's  fluid  (technic 
5.  p.  5).  For  topography  these  slices  are  cut  in  half  through  the  middle  of  the 
uterine  cavity  and  sections  made  through  the  entire  half  organ.  These  are«stained 
with  naematoxylin-picro-acid-fuchsin  (technic  3,  p.  16)  and  mounted  in  balsam. 
For  details  of  the  mucous  membrane  cut  away  most  of  the  muscle  from  around  the 
half  slice,  being  careful  not  to  touch  the  mucous  surface ;  make  thin  sections,  stain 
with  haematoxylin-eosin  (technic  1,  p.  16),  and  mount  in  balsam. 

(2)  Sections  of  the  cervix  may  be  prepared  in  the  same  manner  as  the  preceding. 

(3)  Placental  tissue  may  be  cut  into  small  cubes  and  treated  with  the  same 
technic  (1). 

(4)  If  a  human  or  animal  uterus  with  the  placenta  in  situ  is  obtainable  it 
should  be  cut  into  thin  slices  and  fixed  in  formalin-Midler's  fluid.  The  blocks  of 
tissue  should  be  so  arranged  that  sections  include  the  utero-placental  junction. 
They  may  be  stained  with  haematoxylin-eosin  or  with  haematoxylin-picro-acid-fuch- 
sin  (see  above). 

(5)  Treat  pieces  of  the  human  vagina  according  to  technic  (t,  p.  199). 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 

Nagel:   Das  menschliche  Ei.     Arch.  mik.  Anat.,  Bd.  xxxi.,  [SSS. 

Ruckert:  Zur  Eireifung  derCopepoden.    Anat.  Hefte,  I.  Abth.,  Bd.  iv.,  1894. 

Sobotta:  Ueber  die  Bildung  des  Corpus  luteum  bei  dvr  Mans.  Arch.  mik. 
Anat..  Bd.  xlvii..  1896.— Ueber  die  Bildung  des  Corpus  luteum  beim  Kaninchen. 
Anat.   Hefte,  1.  Abth.,  Bd.  viii.,  [897. 

Hertwig  :  Lehrbuch  der  Entwickelungsgeschichtedes  Menschen  und  der  Wir- 
ere,  Jena.  1896, 

Schaper:  Chapter  on  the  Placenta  in  Stohr's  Text-book  of  Histology,  5th  ed. 

Ballowitz :  Weitere  Beobachtungen  Liber  den  feineren  Bau  <lcr  Saugethier- 
Spermatozoen.     X<it.  f.  wiss,  Z00L,  Bd.  Lii.,  1891. 


CHAPTER    X. 

THE    SKIN    AND    ITS   APPENDAGES. 

The  Skin. 

The  skin  or  cutis  consists  of  two  parts :  (i)  The  derma,  corium, 
or  true  skin,  and  covering  this,  (2)  the  epidermis  or  cuticle.  The 
derma  is  a  connective-tissue  derivative  of  the  mesoderm,  the  epider- 
mis an  epithelial  derivative  of  the  ectoderm. 

The  Derma. — This  is  divided  into  two  layers  which  blend  with- 


(',::  ^-o^.v*.;,-^'.' 


m:' 


—  f 


■ 


D&PW-W'ii 


FlG.  204. —Vertical  Section  of  Thin  Skin,  Human.  X  60.  (Technic  2,  p.  316.)  a,  Epidermis  ; 
l\  pars  papillaris  of  derma;  c,  papillae;  (/,  pars  recticularis  of  derma;  c,  duct  of  sweat 
gland  \  f\  sweat  gland  ;  £-,  subcutaneous  fat. 

out  distinct   demarcation.      The  deeper  is  known  as  the  pars   reticu- 
laris, the  more  superficial  as  the  pars  papillaris  (Fig.  204). 

The  pars  reticularis  is  made  up  of  rather  coarse,  loosely  arranged 


312 


THE   ORGANS. 


white  and  elastic  fibres  with  connective-tissue  cells  in  varying  num- 
bers. The  fibres  run  for  the  most  part  parallel  to  the  surface  of  the 
skin. 

The  pars  papillaris  is  similar   in   structure  to  the   preceding,  but 
both  white  and  elastic  fibres  are  finer  and  more  closely  arranged. 


^ ; 


B\ 


C\ 


!      VVDC 


Fig.  205.— Thick  Vertical  Section  through  Skin  of  Finger  Tip.  (Merkel-Henle.)  .-/,  Corium  ; 
B,  derma  or  cutis  ;  C,  subcutis.  ti,  Stratum  corneum  ;  t>,  duct  of  sweat  gland  ;  c,  stratum 
lucidum;  d,  stratum  germinativum  ;  ^papilla  of  derma;/,  derma ;  g,  blood-vessel :  //, 
sweat  gland  ;  /,  fat  lobule  ;  /,  sweat  pore. 

Externally  this  layer  is  marked  by  minute  folds  which  are  visible  to> 
the  naked  eye,  and  can  be  seen  intersecting  one  another  and  enclos- 
ing small  irregular  areas  of  skin.  In  the  thick  skin  of  the  palms  and 
soles  these  furrows  are  close  together  and  parallel,  while  between 
them  are  long  corresponding  ridges.  In  addition  to  the  furrows  and 
ridges  the  entire  surface  of  the  corium  is  beset  with  minute  papillae. 
These  vary  in  structure,  some  ending  in  a  single  point — simple  pa- 
pilla— others  in  several  points  —  compound  papilla  ;  some  containing 
blood-vessels — vascular  papilla;  others  containing  special  nerve 
terminations — nerve  papilla'  (Fig.  206). 

Smooth  muscle  cells  occur  in  the  corium  in  connection  with  the 
sweat  glands.  In  the  skin  of  the  scrotum — tunica  dartos — and  of  the 
nipple,  the  smooth  muscle  cells  are  arranged  in  a  network  parallel  to 
the  surface.  In  the  face  and  neck  striated  muscle  fibres  penetrate 
the  corium. 

Beneath  the  corium   is  the  subcutaneous  tissue.      This  consists  of 


THE  SKIN  AND  ITS  APPENDAGES.  313 

vertically  disposed  bands  of  connective  tissue — the  retinaculce  cutis — 
which  serve  to  unite  the  corium  to  the  underlying  structures  and 
enclose  fat  lobules.  In  some  parts  of  the  body  this  subcutaneous  fat 
forms  a  thick  layer — the pannicuhis  adiposus. 

The  Epidermis.— This  is  composed  of  stratified  squamous  epi- 
thelium. In  the  comparatively  thin  skin  of  the  general  body  surface 
the  epidermis  is  divided  into  two  sub-layers:  (1)  One  lying  just 
above  the  papillary  layer  of  the  derma,  and  known  as  the  stratum 
germinativum  (stratum  mucosum — stratum  Malpighii) ;  (2)  the  other 
constituting   the  superficial  layer  of   the   skin — the   horny  layer  or 


V 


<  >**— _.v' 


FIG.  206— Froai  Vertical  Section  through  Skin  of  Human  Finger  Tip.  X  200.  (Schafer.)  a, 
Stratum  corneum  ;  3,  stratum  lucidum  ;  r,  stratum  granulosum  ;  d,  stratum  germinati- 
vum. To  the  left  a  vascular  papilla  ;  to  the  right  a  nerve  papilla  containing  tactile  cor- 
puscle. 

stratum  corneum.  In  the  thick  skin  of  the  palms  and  soles  two 
additional  layers  are  developed ;  (3)  the  stratum  granulosum ;  and 
(4)   the  stratum  lucidum  (Fig.  205). 

(i)  The  stratum  germinativum  consists  of  several  layers  of  cells. 
The  deepest  cells  are  columnar  and  form  a  single  layer  (stratum 
cylindricum),  which  rests  upon  a  basement   membrane  separating  it 


3H 


THE   ORG  ASS. 


:W..-. 


<3s 


'/§fv 


from  the  derma.      The  membrane  and  cells  follow  the  elevations  and 
depressions  caused  by  the  papillae.     The  rest  of  the  stratum  germi- 

nativum  consists  of  large  polygonal 
cells.  These  cells  have  well-developed 
intercellular  bridges,  which  appear  as 
spines  projecting  from  the  surfaces  of 
the  cells.  For  this  reason  the  cells  are 
sometimes  called  "prickle"  cells,  and 
the  layer,  the  "  stratum  spinosum. "  The 
spines  cross  minute  spaces  between  the 
cells,  which  are  believed  to  communicate 
with  the  lymph  spaces  of  the  derma 
(Fig.  207,  c). 

(2)  The  stratum  granulosum  is  well 
developed  only  where  the  skin  is  thick. 
It  consists  of  from  one  to  three  layers 
of  flattened  polygonal  cells.  The  pro- 
toplasm of  these  cells  contains  deeply 
staining  granules — keratohyaline  gran- 
ules— which  probably  represent  a  stage 
in  the  formation  of  the  horny  substance 
— keratin — of  the  corneum  cells.  The 
nuclei  of  these  cells  always  show  de- 
generative changes,  and  there  is  reason 
for  believing  that  this  karyolysis  is 
closely  associated  with  the  formation  of 

KrlS     ®  '  ^)   '.  \        the  keratohyaline  granules  (Fig.  207, />). 

(3)  The  stratum  lucidum  is  also  best 
developed  where  the  skin  is  thickest. 
It  consists  of  two  or  three  layers  of 
flat  clear  cells,  the  outlines  of  which 
are  frequently  so  indistinct  that  the 
layer  appears  homogeneous.  The  trans- 
parency of  the  cells  is  due  to  the  pres- 
ence of  a  substance  known  as  clcid'ni,  and  derived  from  the  kerato- 
hyaline granules  of  the  stratum  granulosum  <  Fig.  207,  a). 

(4)  The  stratum  corneum  varies  greatly  in  thickness,  reaching  its 
greatest  development  in  the  skin  of  the  palms  and  soles.  The  cells 
are  flattened  and  horny,  especially  near  their  surfaces.      Some  appear 


-■;- 


"§ 


Wm 


m 


■'& 


&£ 

(&-:/&: 


•'■  few 


V-V 


m 


w 


■  um  >;  <</■■  .■■■■  ■■■ 

"■;')' '  ■.••■■.      ■ 


FIG.  207.— From  Vertical  Section 
through  Thick  Skin.  (Merkel- 
Henle.)  a.  Stratum  lucidum;  />, 
stratum  granulosum  ;  C,  stratum 
germinativum,  showing  intercel- 
lular bridges. 


THE  SKIN  AND  ITS  APPENDAGES.  315 

homogeneous,  others  have  a  lamellated  appearance.  They  contain 
pareleidin,  a  derivative  of  the  eleidin  of  the  stratum  lucidum.  Nu- 
clei are  lost,  but  in  many  of  the  cells  can  be  seen  the  spaces  which 
the  nuclei  once  occupied.  Constant  desquamation  of  these  cells  goes 
on,  cells  from  the  deeper  layers  taking  their  place.  The  cells  of  the 
stratum  germinativum  are  usually  in  a  state  of  active  mitosis. 

The  color  of  the  skin  in  the  white  races  is  due  to  pigmentation  of 
the  deeper  layers  of  the  epidermis.  In  certain  parts  of  the  body 
pigmentation  of  the  connective-tissue  cells  of  the  derma  also  occurs. 
In  the  dark  races  all  cells  of  the  epidermis  are  pigmented,  although 
there  is  less  pigment  in  the  surface  cells  than  in  the  cells  more  deep- 
ly situated. 

Two  kinds  of  glands  occur  in  the  skin — sebaceous  glands  and 
sweat  glands. 

Sebaceous  Glands.  — These  are  usually  associated  with  the  hair 
follicles,  and  will  be  described  in  that  connection.  Sebaceous  glands 
unconnected  with  hair  occur  along  the  margin  of  the  lips,  in  the  glans 
and  prepuce  of  the  penis,  and  in  the  labia  minora. 

Sweat  Glands  {glandules  su  do  rip  a  res). — These  are  found  through- 
out the  entire  skin  with  the  exception  of  the  margin  of  the  lips,  the 
inner"  surface  of  the  prepuce,  and  the  glans  penis.  They  are  simple 
coiled  tubular  glands.  The  coiled  portion  of  the  gland  usually  lies 
in  the  submucosa,  although  it  may  lie  wholly  or  partly  in  the  deeper 
portion  of  the  pars  reticularis.  The  excretory  duct  runs  a  quite 
straight  course  through  the  derma,  and  enters  the  epidermis  in  one 
of  the  depressions  between  the  papillae.  In  the  epidermis  the  duct 
takes  a  spiral  course  to  the  surface,  where  it  opens  into  a  minute 
depression,  just  visible  to  the  naked  eye — the  sweat  pore.  The 
coiled  portion  of  the  gland  is  lined  with' a  simple  cuboidal  epithe- 
lium, having  a  granular  protoplasm.  In  the  smaller  glands  the  epi- 
thelium rests  directly  upon  the  basement  membrane.  In  the  larger 
glands  a  longitudinal  layer  of  smooth  muscle  cells  separates  the 
glandular  epithelium  from  the  basement  membrane.  The  walls  of 
the  ducts  consist  of  two  or  three  layers  of  cuboidal  epithelial  cells, 
resting  upon  a  delicate  basement  membrane,  outside  of  which  are 
longitudinally  disposed  connective-tissue  fibres.  On  reaching  the 
horny  layer  the  epithelial  wall  of  the  duct  ceases,  the  duct  consisting 
of  a  mere  channel  through  the  epithelium. 


i6 


THE   ORGANS. 


TECHNIC. 

(i)  Fix  the  volar  half  of  a  finger-tip  in  formalin-M tiller's  fluid  (technic  5,  p. 
5)  or  in  absolute  alcohol.  Curling  may  be  prevented  by  pinning  to  pieces  of 
cork.  Sections  are  cut  transversely  to  the  ridges,  stained  with  haematoxylin-picro- 
acid-fuchsin  (technic  3.  p.  16),  and  mounted  in  balsam.  Thick  sections  should  be 
cut  for  the  study  of  the  coil  glands  with  their  ducts;  thin  sections  for  cellular  de- 
tails of  the  layers. 

(2)  Prepare  m  the  same  manner  and  for  contrast  with  the  preceding,  sections 
of  thin  skin  from  almost  any  part  of  the  body. 

(3)  Prepare  a  piece  of  negro  skin  in  the  same  manner  and  note  the  position  of 
the  pigment. 

The  Nails. 

The  nails  are  modified  epidermis.  Each  nail  consists  of:  (a)  a 
body,  the  attached  uncovered  portion  of  the  nail;  (/;)  &free  edge,  the 
anterior  unattached  extension  of  the  body ;  (c)  the  nail  root,  the  pos- 
terior part  of  the  nail  which  lies  under  the  skin  (Fig.  208). 

The  nail  lies  upon  a  specially  modified  portion  of  the  corium,  the 
nail  bed,  which  beneath   the  nail  root  and  somewhat  forward  of  the 

e         d 


"-.,        V,..      ■' 


(S 

I  ■-■■  - 


Fig.  :■■>',.  Longitudinal  Section  through  Root  of  Human  Nail  and  Nail  lied.  <  10.  (Schaper.) 
</,  Body  of  nail  ;  l>,  free  edge;  c,  root  of  nail  ;  </,  epidermis;  t\  eponychium  ;  l\  stratum 
germinativumof  matrix  ;  g,  folds  in  derma  of  nail  bed  ;  //,  bone  of  finger  ;  /',  liy pon  vrliium. 

root  is  known  as  the  matrix.  The  nail  bed  is  bounded  on  either  side 
by  folds  of  skin,  the  nail  wall,  while  between  the  nail  wall  and  the 
nail  bed  is  a  furrow,  the  nail  groove  (Fig.  209). 


THE  SKIN  AND  ITS  APPENDAGES. 


317 


The  nail  bed  consists  of  corium.      Its  connective-tissue  fibres  are 
arranged   partly  horizontal  to  the   long  axis  of  the   nail,  partly  in  a 


FIG.  209.— Transverse  Section  of  Nail  and  Nail  Bed.     (Rannie.)     n,  Nail  :  <r,  epidermis  ;  /,  nail 
wall,  to  inner  side  of  which  is  the  nail  groove  ;  /,  folds  of  derma  ;  d,  nail  bed. 

vertical  plane  extending  from  the  periosteum  to  the  nail.  Papillae 
are  not  present,  but  in  their  place  are  minute  longitudinal  ridges, 
which  begin  at  the  matrix  and,  increasing  in  height  as  they  pass  for- 


■Ja7m 


i^^St^^^i.  • 


FIG.  210.— Vertical  Transverse  Section  through  Nail  Body.     X  2S0.     (Szymonowiez.)    a,  Nail  : 
6,  stratum  germinativum  ;  c,  ridge  of  nail  bed  ;  d,  derma  ;  e,  blood-vessel. 


ward,  terminate  abruptly  at  the  end  of  the  nail  bed,  beyond  which 
are  the  usual  papillae  of  the  derma. 

The  nail  itself  consists  of  two  parts — an  outer  harder  part  or  true 
nail,  and  an  under  softer  part.      The  outer  portion  is  hard  and  horny, 


3  iS  THE   ORGANS. 

is  developed  from  the  stratum  lucidum,  and  consists  of  several  layers 
of  clear,  flat,  nucleated  cells.  These  layers  overlap  in  such  a  manner 
that  each  layer  extends  a  little  farther  forward  than  the  layer  above. 
The  under  softer  portion  of  the  nail  corresponds  to  the  stratum 
germinatiyum  of  the  skin  and,  like  the  latter,  consists  of  polygonal 
"  prickle  "  cells  and  a  stratum  cylindricum  resting  upon  a  basement 
membrane.  In  the  matrix  where  the  process  of  nail  formation  is 
going  on,  this  layer  is  thicker  than  elsewhere  and  is  white  and 
opaque  from  the  presence  of  keratohyalin.  The  convex  anterior 
margin  of  this  area  can  be  seen  with  the  naked  eye  and  is  known  as 
the  lunula. 

At  the  junction  of  nail  and  skin,  in  the  nail  groove,  the  stratum 
corneum  extends  somewhat  over  the  nail  as  its  eponychium.  A  simi- 
lar extension  of  the  stratum  corneum  occurs  on  the  under  surface  of 
the  nail  where  the  nail  becomes  free  from  the  nail  bed.  This  is 
known  as  the  hyponychium  (Fig.  208). 

Growth  of  nail  takes  place  by  a  transformation  of  the  cells  of  the 
matrix  into  true  nail  cells.  In  this  process  the  outer  hard  layer  is 
pushed  forward  over  the  stratum  germinativum,  the  latter  remaining 
always  in  the  same  position. 

TECHNIC. 

(1)  Remove  two  or  more  distal  phalanges  from  the  fingers  of  a  new-born  child 
and  fix  in  absolute  alcohol  or  in  formalin-Miiller's  fluid  (technic  5,  p.  5).  After 
fixing,  the  bone  should  be  carefully  removed.  Both  longitudinal  and  transverse 
sections  are  made,  stained  with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  16), 
and  mounted  in  balsam.  In  cutting  the  sections  it  is  usually  best  so  to  place  the 
block  that  the  knife  passes  through  volar  surface  first,  through  nail  last. 

(2)  The  cellular  elements  of  nail  do  not  show  well  in  sections.  For  demon- 
strating the  nail  cells,  boil  a  piece  of  nail  in  concentrated  potash  lye  or  warm  it  in 
strong  sulphuric  acid,  scrape  off  cells  from  the  softened  surface,  and  mount  in 
glycerin. 

The  Hair. 

The  hair,  like  the  nail,  is  a  development  of  the  epidermis.  The 
hair  itself  consists  of  a  shaft,  that  portion  of  the  hair  which  projects 
above  the  skin,  and  a  root,  that  portion  embedded  within  the  skin. 
At  its  lower  end  the  root  presents  a  knob-like  expansion,  the  hair 
bulb,  in  the  under  surface  of  which  is  a  cup-like  depression,  which 
receives  an  extension  of  corium.  This  is  known  as  the  papilla.  En- 
closing the  hair  root  is  the  hair  follicle. 


THE  SKIN  AND  ITS  APPENDAGES. 


3<9 


The  Hair. — This  is  composed  of  epithelial  cells  arranged  in 
three  layers,  which  from  within  outward  are  medulla,  cortex,  and 
cuticle  (Fig.  212). 

(1)  The  medulla  occupies  the  central  axis  of  the  hair.  It  is  ab- 
sent in  small  hairs,  and  in  the  large  hairs  does  not  extend  throughout 
their  entire  length.  It  is  from  16  to  a 
20  fi  in  diameter,  and  consists  of 
from  two  to  four  layers  of  polygonal 
or  cuboidal  cells  with  finely  granular, 
usually  pigmented  protoplasm  and 
rudimentary  nuclei. 

(2)  The  cortex  makes  up  the 
main  bulk  of  the  hair  and  consists 
of  several  layers  of  long  spindle- 
shaped  cells,  the  protoplasm  of  which 
shows  distinct  longitudinal  striations, 
while  the  nuclei  appear  atrophied. 
As  these  striations  give  the  hair  the 
appearance  of  being  composed  of 
fibrillar,  the  term  "  cortical  fibres  " 
has  been  applied  to  them.  In  col- 
ored hair,  pigment  granules  and  pig- 
ment in  solution  are  found  in  and 
between  the  cells  of  this  layer.  This 
pigment  determines  the  color  of  the 
hair.  In  the  root  the  cortical  cells 
are  less  flattened  than  in  the  shaft. 

(3)  The  cuticle  has  a  thickness  of 
about  1  [j.,  and  consists  of  clear  scale- 
like, non-nucleated  epithelial  cells. 
These  overlap  one  another  like 
shingles  on  a  roof,  giving  to  the  sur- 
face of  the  hair  a  serrated  appear- 
ance. 

The  Hair  Follicle. — This  is  also  a  modification  of  the  skin. 
In  the  formation  of  the  follicles  of  the  finer  (lanugo)  hairs  the  epi- 
dermis alone  is  concerned.  The  follicles  of  the  larger  hairs  contain 
both  epidermal  and  dermal  elements.  The  latter  form  the  connec- 
tive-tissue follicle,  while  the  epidermis  forms  the  root  sheaths. 


Fig.  211.— Longitudinal  Section  of  Hair 
and  Its  Follicle  from  Vertical  Section  of 
Scalp.  (Ranvier.)  a,  Shaft  of  hair  ;  />, 
derma;  c,  arrector  pili  muscle;  d,  se- 
baceous gland;  e,  outer  root  sheath; 
f,  inner  root  sheath  ;  g,  connective-tis- 
sue follicle  ;  //,  vitreous  membrane  ;  i, 
hair  bulb;y',  papilla  ;  s,  epidermis. 


THE   ORGANS, 


(i)  The  root  sJicatJi  consists  of  two  sub-layers — the  inner  root 
sheath  and  the  outer  root  sheath  (Figs.  213,  214,  and  215). 

{a)  The  inner  root  sheath  consists  of  three  layers,  which  from 
within  outward  are  the  cuticle  of  the  root  sheath,  Huxley's  layer,  and 
Henle's  layer. 

The  cuticle  of  the  root  sheath  lies  against  the  cuticle  of  the 
hair  and  is  similar  to  the  latter  in  structure.  It  consists  of  thin 
scale-like  overlapping  cells,  nucleated  in  the  deeper  parts  of  the 
sheath,  non-nucleated  nearer  the  surface  (Figs.  213,  214,  and 
215,  c). 

Huxley  s  layer  lies  immediately  outside  the  cuticle  of  the  root 

sheath,  constituting  the  middle  layer  of  the  inner  root  sheath.     It 

consists  of  about  two  rows  of  elongated  cells  with  slightly  granular 

protoplasm  containing  eleidin.      In  the  deeper  portion  of   the   root 

a  b        c  these   cells  contain  nuclei.      Nearer  the 

surface    the    nuclei    are  rudimentary    or 

absent  (Figs.  213,  214,  and  215,  d). 

Henles  layer  is  a  single  row  of  clear 
flat  cells.  In  the  bulb  these  cells  may 
contain  nuclei ;  elsewhere  they  are  non- 
nucleated  (Fig.  215,  e). 

(/;)  The  outer  root  sheath  is  derived 
from  the  stratum  germinativum,  to  which 
it  corresponds  in  structure.  Next  to  the 
vitreous  membrane  is  a  single  layer  of 
columnar  cells  (stratum  cylindricum).  In- 
side of  this  are  several  layers  of  "  prickle" 
cells  (Figs.  213,  214,  and  215,/). 

(2)  The  connective-tissue  follicle  con- 
sists of  three  layers — an  inner  vitreous 
membrane,  a  middle  vascular  layer,  and 
an  outer  fibrous  layer. 

(a)  The  vitreous  or  hyaline  membrane  is  a  thin  homogeneous 
structure  of  the  nature  of  an  elastic  membrane.  It  lies  next  to  the 
outer  root  sheath  and  corresponds  to  the  basement  membrane  of  the 
derma  (Figs.  213,  214,  and  215,^"). 

(b)  The  middle  or  vascular  layer  is  composed  of  fine  connective- 
tissue  fibres,  the  general  arrangement  of  which  is  circular.  Cellular 
elements  are  quite  abundant,  while  elastic  fibres  are  as  a  rule  absent. 


Fig.  212.— Longitudinal  Section  of 
Hair.  350.     (Kolliker.)      n. 

Medulla;  b.  cortex;  r,  cuticle. 


THE  SKIN  AND  ITS  APPENDAGES. 


321 


As  its   name  would   indicate,  this  layer   is   especially  rich   in   blood- 
vessels (Figs.  213,  214,  and  215,  i). 

(c)  The  outer  layer  consists  of  rather  coarse,  loosely  woven  bun- 
dles of  white  fibres,  which  run  mainly  in  a  longitudinal  direction. 
Among:  these  are  elastic  fibres  and  a  few  connective-tissue  cells. 


FlG.  213. — Longitudinal  Section  of  Lower  End  of  Root  of  Hair,  including-  Papilla.  (Kolliker.) 
a,  Root  of  hair  ;  b,  cuticle  of  hair  ;  c,  cuticle  of  root  sheath  ;  </,  Huxley's  layer  of  inner 
root  sheath;  e,  Henle's  layer  of  inner  root  sheath;  /,  outer  root  sheath;  £■,  vitreous 
membrane  ;/j  connective-tissue  follicle;  k,  bulb  of  hair;  /,  papilla. 

In  the  deeper  portion  of  the  root,  some  little  distance  above  the 
bulb,  all  the  layers  of  the  hair  and  its  follicle  can  be  distinctly  seen. 
The  differentiation  of  the  layers  becomes  less  marked  as  one  passes 
in  either  direction.  At  about  the  level  of  the  entrance  of  the  ducts 
of  the  sebaceous  glands  (see  p.  322)  the  inner  root  sheath  disappears, 
and  the  outer  root  sheath  passes  over  into  the  stratum  germinativum 
of  the  skin,  while  between  the  outer  root  sheath  (now  stratum  germi- 
nativum) and  the  hair  are  interposed  the  outer  layers  of  the  skin, 
stratum  granulosum  and  stratum  lucidum,  when  present,  and  stratum 


322 


THE   ORGANS. 


corneum.  All  of  these  are  continuous  with  the  same  layers  of  the 
skin.  In  the  region  of  the  bulb  the  outer  root  sheath  first  becomes 
thinner,  then  disappears,  while  the  layers  of  the  inner  root  sheath 
retain  their  identity  until  the  neck  of  the  papilla  is  reached,  at  which 
point  the  different  layers  coalesce. 

The  arrector pili  muscle  (Fig.  211,6')  is  a  narrow  band  or  bands  of 
smooth  muscle  connected  with  the  hair  follicle.  It  arises  from  the 
outer  layer  of  the  derma  on  the  side  toward  which  the  hair  slants,  and 
is  inserted  into  the  wall  of  the  follicle  at  the  junction  of  its  middle 
and  lower  thirds,  the  sebaceous  gland  being  usually  included  between 
the  muscle  and  the  hair  (see  below).  The  contraction  of  the  mus- 
cle thus  tends  to  straighten  the  hair  and  to  compress  the  gland. 

The  sebaceous  glands  are  with  few  exceptions  connected  with  the 
hair  follicles.     They  are  simple  or  branched  alveolar  glands.     The 


-  ~-> 

•  -^        a 
FIG.  214.— Transverse  Section    through   Root    of  Hair    and  Hair    Follicle.      (K£ 
Hair;  /;,  hair  cuticle;   C,  cuticle  of   root  sheath;  d,   Huxley's  layer;  e,  Henle' 
outer  root  sheath  ;  /,  connective-tissue  follicle. 


Hiker.)    a, 
s  layer ;  /", 


size  of  the  gland  bears  no  relation  to  the  size  of  the  hair,  the  largest 
glands  being  frequently  connected  with  the  smallest  hairs.  The 
glands  are  spherical  or  oval  in  shape  and  each  gland  is  enclosed  by 
a  connective-tissue  capsule  derived  from  the  follicle  or  from  the  der- 


THE  SKIN  AND  ITS  APPENDAGES. 


323 


.       -        ' 


" 


ma.  Beneath  the  capsule  is  a  basement  membrane  continuous  with 
the  vitreous  membrane  of  the  follicle.  The  wide  excretory  duct 
empties  into  the  upper  third  of  the  follicle  and  is  lined  with  stratified 
squamous  epithelium  continuous  with  the  outer  root  sheath  and  stra- 
tum germinativum.  The  lower  end 
of  the  duct  opens  into  several  simple 
or  branched  alveoli,  at  the  mouths  of 
which  the  epithelium  becomes  reduced 
to  a  single  layer  of  cuboidal  cells.  In 
the  alveoli  themselves  the  cells  are 
spheroidal  or  polyhedral,  and  usually 
fill  the  entire  alveolus.  These  cells, 
like  those  lining  the  duct,  are  deriva- 
tives of  the  outer  root  sheath.  The 
secretion  of  the  gland — an  oily  sub- 
stance called  sebum — appears  to  be 
the  direct  product  of  disintegration  of 
the  alveolar  cells,  which  can  usually  be 
seen  in  all  stages  of  the  process  of 
transformation  of  the  cell  into  the 
secretion  of  the  gland.  The  most 
peripheral  cells  show  the  least  secre- 
tory changes,  containing  a  few  small 
fat  droplets.  The  central  cells  and 
those  in  the  lumen  of  the  duct  show 
the  most  marked  changes,  their  proto- 
plasm being  almost  wholly  converted 
into  fat,  their  nuclei  shrunken  or  dis- 
integrated or  lost.  In  the  middle  zone 
are  cells  showing  intermediary  stages 
in  the  process. 

Shedding  of  hair  occurs  in  most 
mammalia  at  regularly  recurring  peri- 
ods.     In  man  there  is  a  constant  death 

and  replacement  of  hair.  In  a  hair  about  to  be  shed,  the  bulb  be- 
comes cornified  and  splits  up  into  a  number  of  fibres.  The  hair 
next  becomes  detached  from  the  papilla  and  from  the  root  sheath 
and  is  cast  off,  the  empty  root  sheaths  collapsing  and  forming  a 
cord  of  cells  between  the  papilla  and  lower  end    of  the  shedding 


Fig.  215.— Prom  Logitudinal  Section 
through  Hair  and  Hair  Follicle.  En- 
larged to  Soo  diameters.  (Schafer.) 
A,  Hair,  a,  Cortex  of  hair;  l\  cu- 
ticle of  hair,  fi,  Inner  sheath,  c, 
Cuticle  of  root  sheath  ;  d,  Huxley's 
layer  ;  e,  Henle's  layer  ;  f,  outer 
root  sheath  ;  £-,  vitreous  membrane; 
i,  connective-tissue  follicle ;  m,  fat 
cells. 


3-4  THE   ORGANS. 

hair.  If  the  dead  hair  is  to  be  replaced  by  a  new  one,  there  sooner 
or  later  occurs  a  proliferation  of  the  cells  of  the  outer  root  sheath 
in  the  region  of  the  old  papilla.  From  this  "  hair  germ  "  the  new 
hair  is  formed  in  a  manner  similar  to  embryonal  hair  formation,  the 
new  hair  growing  upward  under  or  to  one  side  of  the  dead  hair, 
which  it  finally  replaces. 

As  to  the  manner  in  which  growth  of  hair  takes  place,  two  views 
are  held.  According  to  one  of  these,  the  hair,  cuticle,  and  inner 
root  sheath  are  replenished  by  proliferation  of  the  epithelial  cells 
surrounding  the  papilla.  These  parts  thus  grow  from  below  toward 
the  surface.  The  oldest  cells  of  the  outer  root-sheath,  on  the  other 
hand,  lie  against  the  vitreous  membrane,  so  that  growth  of  this  sheath 
takes  place  from  without  inward.  According  to  the  second  view,  the 
various  parts  of  the  hair  and  its  follicle  are  direct  derivatives  of  the 
different  layers  of  the  skin,  and  their  growth  takes  place  by  a  contin- 
uous process  of  invagination.  Thus  the  most  peripheral  cells  of  the 
outer  root-sheath  pass  over  the  papilla  and  turn  upward  to  form  the 
medulla  of  the  hair;  the  stratum  spinosum  of  the  outer  root  sheath 
becomes  continuous  with  the  cortex  of  the  hair ;  the  stratum  lucidum, 
with  the  sheath  of  Henle,  which  turns  up  on  the  hair  as  its  cuticle  ; 
Huxley's  layer,  with  the  cuticle  of  the  inner  root  sheath.  According 
to  this  view  growth  of  hair  is  accomplished  by  continuous  growth 
downward  from  the  surface,  and  turning  up  into  the  hair,  of  these 
layers. 

TECHNIC. 

Pin  out  small  pieces  of  human  scalp  on  cork  and  fix  in  absolute  alcohol  or 
in  formalin-Miiller's  fluid  (technics,  p.  5).  From  one  block  cut  sections  perpen- 
dicular to  the  surface  of  the  scalp  and  in  the  long  axes  of  the  hair  and  follicles. 
From  a  second  block  cut  sections  at  right  angles  to  the  hair  follicles,  i.e.,  not  quite 
parallel  to  the  surface  of  the  scalp  but  a  little  obliquely.  By  this  means  not  only 
are  transverse  sections  secured,  but  if  the  block  be  sufficiently  long  the  follicles 
are  cut  through  at  all  levels.  Sections  are  stained  with  hsematoxylin-picro-acid- 
fuchsin  (technic  3,  p.  16)  and  mounted  in  balsam. 

Blood-vessels  of  the  skin.  From  the  larger  arteries  in  the  subcu- 
taneous tissue  branches  penetrate  the  pars  reticularis  of  the  derma, 
where  they  anastomose  to  form  cutaneous  networks.  The  latter  give 
off  branches,  which  pass  to  the  papillary  layer  of  the  derma  and  there 
form  a  second  series  of  networks,  the  subpapillary,  just  beneath  the 
papillae.  From  the  cutaneous  networks  arise  two  sets  of  capillaries, 
one  supplying  the  fat  lobules,  the  other  supplying  the  region  of  the 


THE  SKIN  AND  ITS  APPENDAGES.  325 

sweat  glands.  From  the  subpapillary  networks  are  given  off  small 
arteries  which  break  up  into  capillary  networks  for  the  supply  of  the 
papillae,  sebaceous  glands,  and  hair  follicles.  The  return  blood  from 
these  capillaries  first  enters  a  horizontal  plexus  of  veins  just  under 
the  papillae.  This  communicates  with  a  second  plexus  just  beneath 
the  first.  Small  veins  from  this  second  plexus  pass  alongside  the 
arteries  to  the  deeper  part  of  the  corium,  where  they  form  a  third 
plexus  with  larger,  more  irregular  meshes.  Into  this  plexus  pass 
most  of  the  veins  from  the  fat  lobules  and  sweat  glands,  although  one 
or  two  small  veins  from  the  sweat  glands  usually  follow  the  duct  and 
empty  into  the  subpapillary  plexus.  The  blood  next  passes  into  a 
fourth  plexus  in  the  subcutaneous  tissue,  from  which  arise  veins  of 
considerable  size.     These  accompany  the  arteries. 

Small  arteries  from  the  plexuses  of  the  skin  and  subcutis  pass 
to  the  hair  follicle.  The  larger  arterioles  run  longitudinally  in  the 
outer  layer  of  the  follicle.  From  these  are  given  off  branches  which 
form  a  rich  plexus  of  small  arterioles  and  capillaries  in  the  vascular 
layer  of  the  follicle.  Capillaries  from  this  plexus  also  pass  to  the 
sebaceous  glands,  the  arrectores  pilorum  muscles,  and  the  papillae. 

The  lymphatics  of  the  skin.  These  begin  as  clefts  in  the  papil- 
lae, which  open  into  a  horizontal  network  of  lymph  capillaries  in 
the  pars  papillaris.  This  communicates  with  a  network  of  larger 
lymph  capillaries  with  wider  meshes  in  the  subcutaneous  tissue. 
The  latter  also  receives  lymph  capillaries  from  plexuses  which  sur- 
round the  sebaceous  glands,  the  sweat  glands,  and  the  hair  follicles. 

The  nerves  of  the  skin.  These  are  mainly  sensory.  Motor 
sympathetic  axones  supply  the  smooth  muscle  of  the  walls  of  the 
blood-vessels  and  of  the  arrectores  pilorum.  The  medullated 
sensory  nerves  are  dendrites  of  spinal  ganglion  cells.  The  larger 
trunks  lie  in  the  subcutis,  giving  off  branches  which  pass  to  the 
corium,  where  they  form  a  rich  subpapillary  plexus  of  both  medul- 
lated and  non-medullated  fibres.  From  the  subcutaneous  nerve- 
trunks  and  from  the  subpapillary  plexus  are  given  off  fibres  which 
terminate  in  more  or  less  elaborate  special  nerve  endings  (see  page 
348).  Their  location  is  as  follows:  (1)  In  tlic  subcutis:  Vater- 
Pacinian  corpuscles,  the  corpuscles  of  Ruffini,  and  the  Golgi-Mazzoni 
corpuscles  of  the  finger-tip.  The  first  two  forms  are  most  numerous 
in  the  palms  and  soles.  (2)  In  the  derma  ;  Tactile  corpuscles  of 
Meissner  and  Wagner.     These  are  found  in  the  papillae,  especially 


326  THE   ORGANS. 

of  the  finger-tip,  palm,  and  sole.  Krause's  end  bulbs — usually  in 
the  derma  just  beneath  the  papillae,  more  rarely  in  the  papillae  them- 
selves. (3)  /;/  the  epithelium  :  Free  nerve  endings  and  tactile  cor- 
puscles. 

Branches  of  the  cutaneous  nerves  supply  the  hair  follicles.  As  a 
rule  but  one  nerve  passes  to  each  follicle,  entering  it  just  below  the 
entrance  of  the  duct  of  the  sebaceous  gland.  As  it  enters  the  follicle 
the  nerve  fibre  loses  its  medullary  sheath  and  divides  into  two 
branches,  which  further  subdivide  to  form  a  ring-like  plexus  of  fine 
fibres  encircling  the  follicle.  From  this  ring,  small  varicose  fibrils 
run  for  a  short  distance  up  the  follicle,  terminating  mainly  in  slight 
expansions  on  the  vitreous  membrane. 

TECHNIC. 

For  the  study  of  the  blood-vessels  of  the  skin  inject  (technic  p.  20)  the  en- 
tire hand  or  foot  of  a  new-born  child.  Examine  rather  thick  sections  either 
mounted  unstained  or  stained  only  with  eosin. 

Development  of  the  Skin,  Nails,  and  Hair. 

The  epidermis  is,  as  already  noted,  of  ectodermic  origin.  It  con- 
sists at  first  of  a  single  layer  of  cuboidal  cells.  This  soon  differen- 
tiates into  two  layers — an  outer,  the  future  stratum  corneum,  and  an 
inner,  the  future  stratum  germinativum.  The  stratum  granulosum 
and  stratum  lucidum  are  special  developments  of  the  stratum  germi- 
nativum. The  corium  is  of  mesoblastic  origin.  It  is  at  first  smooth, 
the  papillae  being  a  secondary  development. 

The  nail  first  appears  as  a  thickening  of  the  stratum  lucidum. 
This  spreads  until  the  future  nail  bed  is  completely  covered.  Dur- 
ing development  the  stratum  corneum  extends  completely  over  the 
nail  as  its  eponychium.  During  the  ninth  month  (intra-uterine)  the 
nail  begins  to  grow  forward  free  from  its  bed  and  the  eponychium  dis- 
appears, except  as  already  noted. 

The  hair  also  develops  from  ectoderm.  It  first  appears  about  the 
end  of  the  third  foetal  month  as  a  small  local  thickening  of  the  epi- 
dermis. This  thickening  is  due  mainly  to  proliferation  of  the  cells 
of  the  stratum  mucosum,  and  soon  pushes  its  way  down  into  the 
underlying  corium,  forming  a  long  slender  cord  of  cells — the  hair 
germ.     Differentiation  of  the  surrounding  connective  tissue  of  the 


THE  SKIN  AND  ITS  APPENDAGES.  327 

corium  forms  the  follicle  wall,  while  an  invagination  of  this  connec- 
tive tissue  into  the  lower  end  of  the  hair  germ  forms  the  papilla. 
The  cells  of  the  hair  germ  now  differentiate  into  two  layers  :  a  central 
core  the  middle  portion  of  which  forms  the  hair,  while  the  peripheral 
portion  forms  the  inner  root  sheath;  and  an  outer  layer  which  be- 
comes the  outer  root  sheath.  The  sublayers  are  formed  from  these 
by  subsequent  differentiation.  The  hair  when  first  formed  lies 
wholly  beneath  the  surface  of  the  skin.  As  the  hair  reaches  the  sur- 
face its  pointed  extremity  pierces  the  surface  epithelium  to  become 
the  hair  shaft. 

The  sebaceous  gland  develops  as  an  outgrowth  from  the  outer 
root  sheath.  This  is  a  flask-shaped  and  at  first  solid  mass  of 
cells,  which  later  differentiate  to  form  the  ducts  and  alveoli  of  the 
gland. 

The  sweat  glands  first  appear  as  solid  ingrowths  of  the  stratum 
germinativum  into  the  underlying  corium.  The  lower  end  of  the 
ingrowth  becomes  thickened  and  convoluted  to  form  the  coiled  por- 
tion of  the  gland,  and  somewhat  later  the  central  portion  becomes 
channelled  out  to  form  the  lumen.  The  muscle  tissue  of  the  sweat 
glands,  which  lies  between  the  epithelium  and  the  basement  mem- 
brane, is  the  only  muscle  of  the  body  derived  from  the  ectoderm. 

The  Mammary  Gland. 

The  mammary  gland  is  a  compound  alveolar  gland.  It  consists 
of  from  fifteen  to  twenty  lobes,  each  of  which  is  subdivided  into 
lobules.  The  gland  is  surrounded  by  a  layer  of  connective  tissue 
containing  more  or  less  fat.  From  this  periglandular  connective 
tissue  broad  septa  extend  into  the  gland,  separating  the  lobes  (inter- 
lobar septa).  From  the  latter  finer  connective-tissue  bands  pass 
in  between  the  lobules  (interlobular  septa).  From  the  interlobular 
septa  strands  of  connective  tissue  extend  into  the  lobule  where  they 
act  as  support  for  the  glandular  structures  proper.  An  excretory  duct 
passes  to  each  lobe  where  it  divides  into  a  number  of  smaller  ducts 
(lobular  ducts),  one  of  which  runs  to  each  lobule.  Within  the  latter 
the  lobular  duct  breaks  up  into  a  number  of  terminal  ducts,  which  in 
turn  open  into  groups  of  alveoli.  The  fifteen  to  twenty  main  excre- 
tory ducts  pass  through  the  nipple  and  open  on  its  surface.  At  the 
base  of  the  nipple  each  main  duct  presents  a  sac-like  dilatation,  the 


328  THE   ORGANS. 

ampulla,  which  appears  to  act  as  a  reservoir  for  the  storage  of  the 
milk. 

Until  puberty  the  gland  continues  to  develop  alike  in  both  sexes, 
but  after  about  the  twelfth  year  the  male  gland  undergoes  retrogres- 
sive changes,  while  the  female  gland  continues  its  development. 

The  inactive  mammary  gland,  by  which  is  meant  the  female 
gland  up  to  the  advent  of  the  first  pregnancy  and  between  periods  of 
lactation,  consists  mainly  of  connective  tissue  and  a  few  scattered 
groups  of  excretory  ducts  (Fig.  216).  Around  the  ends  of  some  of 
the  ducts  are  small  groups  of  collapsed  alveoli.  Both  ducts  and 
alveoli  are  lined  with  a  low  columnar,  often  rather  flat  epithelium. 

The  Active  Mammary  Gland. — Throughout  pregnancy  the 
gland  undergoes  extensive  developmental  changes  and  becomes  func- 
tional at  about  the  time  of  birth  of  the  child.     The  microscopic  ap- 


Fig.  216.    Prom  Section  of  Human  Inactive  Mammary  Gland,   x  25.  (Technic  1,  p.  331.)    Gland 
composed  almost  wholly  of  connective  tissue  ;  few  scattered  groups  of  tubules. 

pearance  of  the  active  gland  differs  greatly  from  that  of  the  inac- 
tive (Fig.  217).  There  is  a  marked  reduction  in  the  connective 
tissue  of  the  gland,  its  place  being  taken  by  newly  developed  ducts 
and  alveoli.      The  alveoli  are  spheroidal,  oval,  or  irregular  in  shape, 


THE  SKIN  AND  ITS  APPENDAGES. 


329 


and  vary  considerably  in  size.  The  alveoli  are  lined  by  a  single 
layer  of  low  columnar  or  cuboidal  epithelial  cells  which  rest  upon  a 
homogeneous  basement  membrane.  The  appearance  of  the  cells  dif- 
fers according  to  their  secretory  conditions.  The  resting  cell  is  cu- 
boidal and  its  protoplasm  granular.  With  the  onset  of  secretion  the 
cell  elongates,  and  a  number  of  minute  fat  droplets  appear.  These 
unite  to  form  one  or  two  large  globules  of  fat  in  the  free  end  of  the 
cell.      The  fat  is  next  discharged  into  the  lumen  of  the  alveolus,  and 


r 


S^MJS?*^!?*? 


}•■■■■-■■     '■    ■■y:-:,i.i-    :    ■    :  :--:  -•-    -'   -  -  -     "  - 


■&i£ 


;  V  A  IIP!  yfWBBS^ 

FlG.  217.— From  Section  of  Human  Mammary  Gland  during'  Lactation.     X  50.      CStohr.) 
Branch  of  excretory  duct ;  6,  interlobular  connective  tissue  ;  c,  alveoli. 


regeneration  of  the  cell  takes  place  from  the  unchanged  basal  por- 
tion. As  to  the  number  of  times  a  cell  is  able  to  go  through  this 
process  of  secretion  and  repair  before  it  must  be  replaced  by  a  new 
cell,  nothing  definite  is  known.  Active  secretion  does  not  as  a  rule 
take  place  in  all  the  alveoli  of  a  lobule  at  the  same  time.  Each  lob- 
ule thus  contains  both  active  and  inactive  alveoli.  The  smallest 
ducts  are  lined  with  a  low  columnar  or  cuboidal  epithelium.  This 
increases  in  height  with  increase  in  the  diameter  of  the  duct  until  in 
the  largest  ducts  the  epithelium  is  of  the  high  columnar  type. 

The  secretion  of  the  gland  is  milk.  This  consists  microscopically 
of  a  clear  fluid  or  plasma  in  which  are  suspended  the  milk  globules. 
The  latter  are  droplets  of  fat  from  3  to  5  :>■  in  diameter,  each  enclosed 


330 


THE   ORGANS. 


in  a  thin  albuminous  membrane  which  prevents  the  droplets  from 
coalescing".  Cells,  probably  leucocytes,  containing  fat  droplets  may 
also  be  present.  In  the  secretion  of  the  gland  during  the  later 
months  of  pregnancy,  and  also  for  a  few  days  following  the  birth  of 


Fig.  218.— From  Section  of  Mammary  Gland  of  Guinea-pig-  during  Lactation.  X  500.  (Osmic 
acid.)  (Szymonowicz.)  ii,  Basement  membrane;  />,  lumen  of  alveolus;  c,  tangential  sec- 
tion of  alveolus;  d,  fat  globules. 


the  child,  a  relatively  large  number  of  large  fat-containing  leucocytes 
— colostrum  corpuscles — are  found. 

Blood-vessels. — These  enter  the  gland,  branch  and  ramify  in  the 
interlobar  and  interlobular  connective  tissue,  and  finally  terminate  in 
capillary  networks  among  the  alveoli  and  ducts.  From  the  capillaries 
arise  veins  which  accompany  the  arteries. 

Lymphatics. — Lymph  capillaries  form  networks  among  the  alveoli 
and  terminal  ducts.  The  lymph  capillaries  empty  into  larger  lym- 
phatics in  the  connective  tissue.  These  in  turn  communicate  with 
several  lymph  vessels  which  convey  the  lymph  to  the  axillary  glands. 

Nerves. — Both  cerebro-spinal  and  sympathetic  nerves  supply  the 
gland,  the  larger  trunks  following  the  interlobar  and  interlobular 
connective-tissue  septa.  The  nerve  terminals  break  up  into  plexuses 
which  surround  the  alveoli  just  outside  their  basement  membranes. 


THE  SKIN  AND  ITS  APPENDAGES.  331 

From  these  plexuses,  delicate  fibrils  have  been  described  passing 
through  the  basement  membrane  and  ending  between  the  secreting 
cells. 

Development. — The  development  of  the  mammary  gland  is  quite 
similar  to  the  development  of  the  sebaceous  glands.  The  gland  first 
appears  as  a  dipping  down  of  solid  cord-like  masses  of  cells  from  the 
stratum  mucosum.  The  alveoli  remain  rudimentary  until  the  advent 
of  pregnancy.  After  lactation  the  alveoli  atrophy,  being  replaced  by 
connective  tissue,  and  the  gland  returns  to  the  resting  state.  After 
the  menopause  a  permanent  atrophy  of  the  gland  begins,  fat  and  con- 
nective tissue  ultimately  almost  wholly  replacing  the  glandular  ele- 
ments. 

TECHNIC. 

(1)  Fix  thin  slices  of  an  inactive  mammary  gland  in  formalin-Muller's  fluid 
(technic  5,  p.  5).  Stain  sections  with  haematoxylin-eosin  (technic  1,  p.  16),  and 
mount  in  balsam. 

(2)  Prepare  sections  of  an  active  mammary  gland,  as  in  preceding  technic  (1). 

(3)  Fix  very  thin  small  pieces  of  an  active  gland  in  one-per-cent  aqueous  solu- 
tion of  osmic  acid.  After  twenty-four  hours  wash  in  water  and  harden  in  graded 
alcohols.  Thin  sections  may  be  mounted  unstained,  or  after  slight  eosin  stain,  in 
glycerin. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 
Ranvier:  Traite  Technique  d'Histologie. 
Schafer:  Essentials  of  Histology. 

Spalteholz :  Die  Vertheilung  der  Blutgefasse  in  der  Haut.  Arch.  Anat.  u. 
Phys.,  Anat.  Abth.,  1S93. 

McMurrick  :  Development  of  the  Human  Body. 


CHAPTER    XL 

THE   NERVOUS   SYSTEM. 

The  nervous  mechanism  in  man  consists  of  two  distinct  though 
associated  systems,  the  cerebrospinal  nervous  system  and  the  sym- 
pathetic nervous  system.  Each  of  these  systems  is  composed  of  a 
central  portion  (which  is  its  centre  of  nervous  activity)  and  of  a  per- 
ipheral portion  (which  serves  to  place  the  centre  in  connection  with 
the  organs  which  it  controls).  In  the  cerebro-spinal  system  the  cen- 
tral portion  is  known  as  the  central  nervous  system  and  consists  of 
the  cerebro-spinal  axis,  or  brain  and  spinal  cord.  The  peripheral 
portion  is  formed  by  the  cranial  and  spinal  nerves.  The  central  por- 
tion of  the  sympathetic  system  consists  of  a  series  of  ganglia  from 
which  the  sympathetic  nerves  take  origin.  These  latter  constitute 
its  peripheral  portion. 

Histological  Development. 

The  beginning  differentiation  of  the  nervous  system  appears  very 
early  in  embryonic  life.  There  is  first  the  formation  of  a  groove  or 
furrow  in  the  outer  embryonic  layer,  or  ectoderm.  This  is  known  as 
the  neural  groove.  On  either  side  of  this  groove  is  an  elevation  — 
the  neural  fold.  By  the  dorsal  union  of  these  folds  the  neural  groove 
is  converted  into  the  neural  tube.  The  lumen  of  the  neural  tube 
corresponds  to  the  central  canal  of  the  cord  and  the  ventricles  of  the 
brain  in  the  adult,  and  it  is  from  the  ectodermic  cells  which  form  the 
walls  of  this  tube  that  the  entire  nervous  system  is  developed.  At 
that  end  of  the  neural  tube  which  corresponds  to  the  head  of  the 
embryo  the  greatest  development  takes  place.  Here  are  early  formed 
the  three  primary  cerebral  vesicles.  These  are  known  respectively 
as  the  forcbrain  (anterior  cerebral  vesicle — prosencephalon),  the 
midbrain  (middle  cerebral  vesicle- — mesencephalon),  and  the  Iiiud- 
brain  (posterior  cerebral  vesicle — rhombencephalon).  From  the  an- 
terior cerebral  vesicle  are  developed  the  cerebral  hemispheres,  the 

332 


THE  NERVOUS  SYSTEM.  333 

corpus  striatum.,  the  optic  thalamus,  and  posteriorly  as  far  as  the 
anterior  corpora  quadrigemina.  From  the  middle  cerebral  vesicle 
are  developed  the  corpora  quadrigemina  and  the  cerebral  peduncles. 
From  the  posterior  cerebral  vesicle  are  developed  the  cerebellum, 
pons,  and  medulla  oblongata.  From  the  remainder  of  the  neural 
tube  is  formed  the  spinal  cord. 

The  wall  of  the  neural  tube  is  at  first  composed  of  a  single  layer 
of  epithelial  cells.  By  proliferation  of  these  cells  the  epithelium 
soon  becomes  many-layered,  although  some  of  the  original  epithelial 
cells  still  extend  through  the  entire  thickness  of  the  wall. 

Some  of  the  cells  which  extend  through  the  entire  thickness  of 
the  wall  of  the  neural  tube  {spongioblasts  of  His)  increase  in  length 
as  the  wall  increases  in  thickness.  The  inner  ends  of  these  cells 
form  the  lining  of  the  tube,  while  the  parts  of  the  cells  between  the 
lumen  and  the  nuclei  tend  to  collapse,  forming  cord-like  structures. 
The  outer  ends  of  the  cells,  on  the  other  hand,  become  perforated 
and  unite  to  form  a  thick  network — the  marginal  veil  of  His.  Of 
these  cells,  some  retain  this  position  in  the  adult  and  are  known  as 
epcndymal  cells;  others  move  away  from  the  central  canal  and  be- 
come neuroglia  cells.  Other  of  the  cells  which  form  the  wall  of  the 
neural  tube  also  develop  into  various  forms  of  glia  cells. 

Still  other  of  the  cells  of  the  neural  tube  are  the  ancestors  of  the 
neurones,  and  as  such  are  known  as  neuroblasts.  From  the  outer 
end  of  the  neuroblast  a  process  grows  out — the  future  axone.  Den- 
drites which  at  this  stage  are  absent  develop  later  in  a  similar  man- 
ner, i.e. ,  by  extensions  of  the  cell  protoplasm.  The  neuroblasts  soon 
leave  their  original  position  near  the  central  canal  and  pass  outward 
along  the  spaces  between  the  elongated  ependymal  cells.  The  direc- 
tions which  these  neuroblasts  take  seem  to  be  determined  largely  by 
the  lines  of  least  resistance  offered  by  the  network  of  the  marginal 
veil.  A  large  number  of  these  cells  pass  ventrally,  their  axones 
piercing  the  marginal  veil  and  leaving  the  cord  as  the  ventral  root 
fibres.  Other  neuroblasts  pass  laterally  and  dorsally.  The  axones 
of  these  neuroblasts  seem  to  meet  such  opposition  in  the  marginal 
veil  that  they  do  not  pierce  it,  but  are  directed  upward  and  downward 
within  the  cord.  Later  becoming  medullated,  these  axones  consti- 
tute many  of  the  fibres  of  the  white  matter  of  the  cord. 

During  the  closure  of  the  neural  groove,  groups  of  cells  from  the 
crest  of  each  neural  fold  become  separated  from  the  rest  of  the  de- 


334  THE   ORGANS. 

veloping  nervous  system.  From  these  are  formed  the  spinal  ganglia. 
The  ganglia  of  the  sympathetic  system  are,  according  to  His,  formed 
of  cells  which  pass  out  from  the  spinal  ganglia  to  the  positions  occu- 
pied later  by  the  sympathetic  ganglia.  According  to  others  some  of 
the  cells  of  the  sympathetic  ganglia  may  be  derived  from  cells  which 
migrate  from  the  neural  tube  along  the  ventral  roots. 


Membranes   of  The  Brain  and  Cord. 

The  brain  and  cord  are  enclosed  by  two  connective-tissue  mem- 
branes, the  dura  mater  and  the  pia  mater. 

The  dura  mater  is  the  outer  of  the  two  membranes  and  consists 
of  dense  fibrous  tissue.  The  cerebral  dura  serves  both  as  an  invest- 
ing membrane  for  the  brain  and  as  periosteum  for  the  inner  surfaces 
of  the  cranial  bones.  It  consists  of  two  layers  :  (a)  An  inner  layer 
of  closely  packed  fibro-elastic  tissue  containing  many  connective- 
tissue  cells,  and  lined  on  its  brain  surface  with  a  single  layer  of  flat 
cells;  and  (/?)  an  outer  layer,  which  forms  the  periosteum  and  is 
similar  in  structure  to  the  inner  layer,  but  much  richer  in  blood-ves- 
sels and  nerves.  Between  the  two  layers  are  large  venous  sinuses. 
The  spinal  dura  corresponds  to  the  inner  layer  of  the  cerebral  dura, 
which  it  resembles  in  structure,  the  vertebrae  having  their  own  sep- 
arate periosteum.  The  outer  surface  of  the  spinal  dura  is  covered 
with  a  single  layer  of  flat  cells,  and  is  separated  from  the  periosteum 
by  the  epidural  space,  which  contains  anastomosing  venous -channels 
lying  in  an  areolar  tissue  rich  in  fat. 

The  pia  mater  closely  invests  the  brain  and  cord,  extending  into 
the  sulci  and  sending  prolongations  into  the  ventricles.  It  consists 
of  fibro-elastic  tissue  arranged  in  irregular  lamellae,  forming  a  spongy 
tissue,  the  cavities  of  which  contain  more  or  less  fluid.  The  outer 
lamellae  are  the  most  compact,  and  are  covered  on  the  dural  surface 
by  a  single  layer  of  flat  cells.  It  is  this  external  layer  of  the  pia 
which  is  frequently  described  as  a  separate  membrane,  the  arachnoid. 
The  inner  lamellae  of  the  pia  are  more  loosely  arranged,  are  more 
cellular  and  more  vascular.  Especially  conspicuous  are  large,  irregu- 
lar cells  with  delicate  bodies  and  large  distinct  nulcei.  They  lie  upon 
the  connective-tissue  bundles  partially  lining  the  spaces. 

The  Pacchionian  bodies  are  peculiar  outgrowths  from  the  outer 
layer  of   the   pia  mater  cerebralis,  which  are  most  numerous  along 


THE  NERVOUS  SYSTEM. 


335 


the  longitudinal  fissure.     They  are  composed  of  fibrous  tissue,  and 
frequently  contain  fat  cells  and  calcareous  deposits. 

Blood-vessels. — The  spinal  dura  and  the  inner  layer  of  the  cere- 
bral dura  are  poor  in  blood-vessels.  The  outer  layer  of  the  cerebral 
dura,  forming  as  it  does  the  periosteum  of  the  cranial  bones,  is  rich 
in  blood-vessels  which  pass  into  and  supply  the  bones.  The  pia  is 
very  vascular,  especially  its  inner  layers,  from  which  vessels  pass 
into  the  brain  and  cord. 

TECHNIC. 

For  the  study  of  the  structure  of  the  membranes  of  the  brain  and  spinal  cord, 
fix  pieces  of  the  cord  with  its  membranes,  and  of  the  surface  of  the  brain  with  mem- 
branes attached,  in  formalin-Muller's  fluid  (technic  5,  p.  5)  and  stain  sections  with 
haematoxylin-eosin  (technic  1,  p.  16). 

THE    GANGLIA. 

Ganglia  are  collections  of  nerve  cells  which  are  connected  with 
the  peripheral  nerves.  Each  ganglion  is  surrounded  by  a  connective- 
tissue  capsule  which  is  continuous  with  the  perineurium.      From  this 


Fig.  219.— Longitudinal  Section  through  a  Spinal  Ganglion.  X  20.  (Stohr.)  .7,  Ventral 
nerve  root;  fr,  dorsal  nerve  root  ;  c,  mixed  spinal  nerve;  d,  groups  of  ganglion  cells;  e, 
nerve  fibres  ;  f,  perineurium  ;  g,  fat ;  //,  blood-vessel. 


capsule  connective-tissue  trabecules  extend  into  the  ganglion,  forming 
a  connective-tissue  framework.     Within  the  ganglion  the  nerve  cells 


336 


THE   ORGANS. 


are  separated  into  irregular  groups  by  strands  of  connective  tissue 
and  by  bundles  of  nerve  fibres.  Ganglia  are  of  two  kinds  :  those  of 
the  cerebro-spinal  system  and  those  of  the  sympathetic  system. 

Cerebro-Spinal  Ganglia  (Fig.  219). — The  spinal  ganglia  lie 
on  the  dorsal  roots  of  the  spinal  nerves  between  their  exit  from  the 
cord  and  their  union  with  the  ventral  roots.  The  cerebral  ganglia 
occupy  an  analogous  position  relative  to  the  cranial  nerves.  The 
ganglion  cells  are  large  and  spherical  (Fig.  220).  Each  contains 
a  centrally  located  nucleus  and  a  distinct  nucleolus,  and  is  surrounded 
by  a  capsule  of  flat,  concentrically  arranged  connective-tissue  cells 
(Fig.  220,  s).  Stained  by  Nissl's  method  the  cytoplasm  is  seen  to 
contain  rather  small,  finely  granular  chromophilic  bodies,  which  show 
a  tendency  to  concentric  arrangement  around  the  nucleus.  Pigmen- 
tation is  common.  According  to  Dogiel  (Fig.  221)  there  are  two 
distinct  types  of  ganglion  cells:  (1)  Unipolar  ganglion  cells,  the 
single  process  of  which  divides,  one  branch  entering  the  cord  as  one 


'  '   •  '    •  i.-::\ 


M 


h   :':-pSS 


t-~p, 


wf * 


3r-y 


FIG.  220.—  Large  Spinal  Ganglion  Cell  from  Human  Spinal  Ganglion  showing  Connective- 
tissue  Capsule.  (From  Barker,  after  von  Lenhossek.)  s,  Capsule;  />,  peripheral  zone  of 
1  [ear  cytoplasm  ;  />',  axone  hill  ;  «,  axone ;  //,  pigment. 


of  the  fibres  of  a  dorsal  nerve  root,  the  other  becoming  a  fibre  of  a 
peripheral  nerve.  (2)  Unipolar  ganglion  cells,  the  single  process  of 
which  almost  immediately  splits  up  into  many  fine  mcdullated  fibres. 
These  remain  within  the  ganglion  and  end  in  dense  felt  works  around 


THE  NERVOUS   SYSTEM. 


337 


other  spinal  ganglion  cells.  A  few  multipolar  cells  are  also  described 
as  occurring  in  the  spinal  ganglia.  In  addition  to  the  processes  of 
these  ganglion  cells,  most  of  which  are  medullated  and  which  make 


Fig.  221.— Scheme  of  Neurone  Relations  within  a  Spinal  Ganglion,  according  to  Dogiel. 
(Barker.)  A,  Ventral  root;  B,  dorsal  root;  C,  spinal  nerve  ;  D,  ventral  division,  E,  dor- 
sal division  of  spinal  nerve  ;  F,  communicating  branch  to  sympathetic  ;  a,  spinal  gaDglion 
cell  of  first  type,  the  main  process  of  which  (//)  divides,  one  arm  passing  centrally  as  a 
fibre  of  the  dorsal  root,  the  other  peripherally  as  an  afferent  fibre  of  the  mixed  spinal 
nerve  ;  o,  spinal  ganglion  cell  of  second  type,  the  axone  of  which  (u)  ends  in  a  pericellular 
network  around  the  bodies  of  cells  of  the  first  type  ;  .f,  sympathetic  fibres  ending  in 
plexuses  around  the  bodies  of  cells  of  the  second  type. 


up  the  main  mass  of  fibres  of  the  ganglia,  there  are  also  a  few  fine 
non-medullated  fibres  which  come  from  cells  in  adjacent  sympathetic 
ganglia  and  end  in  arborizations  around  the  spinal  ganglion  cells. 
Dogiel  believes  that  these  end  entirely  around  cells  of  the  second 
type. 

The  relation  of  the  spinal  ganglion  cell  to  the  dorsal  roots  is  de- 
scribed on  page  351. 

The  Sympathetic  Ganglia. — The  larger  ganglia  resemble  the 
spinal  ganglia  in  having  a  connective-tissue  capsule  and  framework. 


338  THE   ORGANS. 

The  cells  are  smaller  and  often  densely  pigmented.  Each  cell  is  sur- 
rounded by  a  capsule  of  flat  connective- tissue  cells,  but  the  capsule 
is  not  so  thick  and  distinct  as  that  of  the  spinal  ganglion  cell.  Most 
of  the  cells  are  multipolar.  The  fibres  which  traverse  these  ganglia 
are  mainly  of  the  non-medullated  variety.  Sympathetic  ganglion 
cells  are  not  confined,  however,  to  definite  ganglionic  structures,  but 
occur  in  ill-defined  groups  in  certain  of  the  viscera,  e.g.,  in  the  heart 
and  in  the  intestinal  plexuses  of  Meissner  and  Auerbach.  Groups  of 
two  or  three  cells,  or  even  single  cells,  are  also  found  scattered  along 
the  sympathetic  nerves.  Such  cells  show  great  variation  in  shape, 
size,  and  internal  structure. 

TECHNIC. 

(i)  Fix  spinal  and  sympathetic  ganglia  in  formalin-AIiiller's  fluid  (technic  5,  p. 
5).  Stain  sections  with  haematoxylin-eosin  (technic  1,  p.  16),  or  with  lnematoxylin- 
picro-acid  fuchsin  (technic  3,  p.  16). 

(2)  Fix  spinal  and  sympathetic  ganglia  in  absolute  alcohol  or  in  ten-per-cent 
formalin,  and  stain  sections  by  Nissl's  method  (technic,  p.  28). 

(3)  See  also  technic  1,  p.  356. 

THE   PERIPHERAL   NERVES. 

The  peripheral  nerves  are  divided  into  spinal  nerves  and  cranial 
nerves,  the  former  taking  origin  from  the  cord,  the  latter  from  higher 
centres.  Each  spinal  nerve  consists  of  two  parts — a  motor  or  effer- 
ent part  and  a  sensory  or  afferent  part.  Of  the  cranial  nerves  some 
are  purely  efferent,  others  purely  afferent,  while  still  others  consist 
like  the  spinal  nerves  of  both  efferent  and  afferent  fibres.  The 
efferent  fibres  of  the  spinal  nerves  are  axones  of  cell  bodies  situated 
in  the  anterior  horns  of  the  cord  (see  p.  353,  and  Figs.  227  and 
236).  They  leave  the  cord  as  separate  bundles,  which  join  to  form 
the  motor  or  efferent  root.  The  afferent  fibres  are  dendrites  of  cell 
bodies  situated  in  the  spinal  ganglia  (see  p.  347  and  Figs.  227  and 
236).  These  leave  the  ganglion  and  join  with  the  fibres  of  the  motor 
root  to  form  the  mixed  spinal  nerve  (Fig.  227,/).  The  connection  of 
the  ganglion  with  the  cord  is  by  means  of  the  axones  of  the  spinal 
ganglion  cells,  which  enter  the  cord  as  the  posterior  root  (Fig.  236). 
Among  the  afferent  fibres  of  the  posterior  root  are  also  found  a  few 
efferent  fibres  (Fig.  227,  c). 

The  peripheral  nerve  consists  of  nerve  fibres  supported  by  con- 
nective tissue  (Fig.  222).      Enclosing  the  entire  nerve  is  a  sheath  of 


THE  NERVOUS   SYSTEM. 


339 


dense  connective-tissue,  the  epineurium.  This  sends  septa  into  the 
nerve  which  divide  the  fibres  into  a  number  of  bundles  or  fascicles. 
Surrounding  each  fascicle  the  connective  tissue  forms  a  fairly  distinct 
sheath,  the  perifascicular  shcatJi  or  perineurium.  From  the  latter, 
delicate  strands  of  connective  tissue  pass  into  the  fascicle,  separating 
the  individual  nerve  fibres.      This  constitutes  the  intrafascicular  con- 


FlG.  222.— From  Transverse  Section  of  Human  Nerve  Trunk.  (Osmicacid  fixation.)  (Ouain.) 
ep,  Nerve  sheath  or  epineurium  surrounding  the  entire  nerve  and  containing  blood-ves- 
sels (z>)  and  small  groups  of  fat  cells  (/")  ;  per,  perifascicular  sheath  or  perineurium  sur- 
rounding each  bundle  or  fascicle  of  nerve  fibres;  end,  interior  of  fascicle  showing  sup- 
porting connective  tissue,  the  endoneurium. 


ncctivc  tissue  or  endoneurium.  In  the  connective-tissue  layers  of  the 
perineurium  are  lymph  spaces  lined  with  endothelium,  which  com- 
municate with  lymph  channels  within  the  fascicle.  When  nerves 
branch,  the  connective-tissue  sheaths  follow  the  branchings.  When 
the  nerve  becomes  reduced  to  a  single  fibre,  the  connective  tissue 
still  remaining  constitutes  the  sheath  of  Henle  (see  Fig.  66,  p. 
108).  For  description  of  medullated  and  non-medullated  nerve  fibres 
see  pages  107  and  108. 

For  sensory  nerve  terminations  see   page  348 ;   for  motor   nerve 
terminations  see  page  353. 


14-0  THE   ORGAXS. 


TECHNIC. 

Fix  a  medium-sized  nerve,  such  as  the  human  radial  or  ulnar,  by  suspending 
it.  with  a  weight  attached  to  the  lower  end,  in  formalin- Midler's  fluid  (technic  5,  p. 
5).  Stain  transverse  sections  in  hasmatoxylin-picro-acid  fuchsin  (technic  3,  p.  16) 
and  mount  in  balsam. 

THE   SPINAL   CORD. 

The  spinal  cord  encased  in  its  membranes  lies  loosely  in  the  ver- 
tebral canal,  extending  from  the  upper  border  of  the  first  cervical 
vertebra  to  the  middle  or  lower  border  of  the  first  lumbar  ver- 
tebra. It  is  cylindrical  in  shape  and  continuous  above  with  the 
medulla  oblongata,  while  below  it  terminates  in  a  slender  cord,  the 
filum  terminate.  At  two  levels,  one  in  the  cervical  and  one  in  the 
lumbar  region,  the  diameter  of  the  cord  is  considerably  increased. 
These  are  known  respectively  as  the  cervical  and  lumbar  eulaigc- 
tnents.  The  spinal  nerve  roots  leave  the  cord  at  regular  intervals, 
thus  indicating  a  division  of  the  cord  into  segments,  each  segment 
extending  above  and  below  its  nerve  roots  one-half  the  distance  to 
the  next  adjacent  roots.  There  are  3 1  segments  corresponding  to 
the  31  spinal  nerves;  8  cervical,  12  dorsal,  5  lumbar,  5  sacral,  and  1 
coccygeal. 

If  the  fresh  cord  be  cut  through,  it  is  seen  to  consist  of  a  central 
gray  matter  surrounded  by  a  peripheral  zone  of  white  matter.  The 
difference  in  color  is  due  to  the  fact  that  the  peripheral  zone  is  com- 
posed almost  entirely  of  medullated  nerve  fibres  with  their  white 
myelin  sheaths,  while  the  gray  matter  is  comparatively  poor  in 
medullated  fibres,  consisting  mainly  of  nerve  cell  bodies  and  their 
dendritic  processes.  The  greater  vascularity  of  the  gray  matter  also 
contributes  to  its  color. 

The  internal  structure  of  the  cord  can  be  best  studied  by  means 
of  transverse  sections  taken  at  different  levels. 

TECHNIC. 

(i)  Carefully  remove  the  cord  (human  if  possible;  if  not,  that  of  a  large  dog) 
with  its  membranes,  cut  into  two  or  three  pieces  if  necessary,  and  lay  on  sheet 
cork.  Slit  the  dura  along  one  side  of  the  cord,  lay  the  folds  back,  and  pin  the 
dura  to  the  cork.  Care  must  be  taken  to  leave  the  dura  very  loose,  otherwise  it 
will  flatten  the  cord  as  it  shrinks  in  hardening.  With  a  sharp  razor  now  cut  the 
cord,  but  not  the  dura,  into  segments  about  1  cm.  thick.  Fix  for  two  weeks  in 
Midler's  fluid,  wasli  in  water  to  which  a  little  formalin  has  been  added,  harden  in 


THE  NERVOUS   SYSTEM.  341 

graded  alcohols.     Pieces  of  the  cord  may  be  cut  out  as  wanted  and  embedded  in 
celloidin.     Sections  should  be  cut  about  15  u  in  thickness. 

(2)  For  the  study  of  the  general  internal  structure  of  the  cord,  stain  a  section 
through  the  lumbar  enlargement  of  a  cord  prepared  according  to  the  preceding 
technic  (1)  in  haematoxylin-picro-acid  fuchsin  (technic  3,  p.  16)  and  another  section 
through  the  same  level  in  Weigert"s  hematoxylin  (technic  p.  25J.  Mount  both  in 
balsam. 

Practical  Study. 

Section    Through    the    Lumbar    Enlargement  (Fig.  223. — 
The  general   features  of  the   section  can  be  best   seen  with   the 

naked  eye  or  with  a  low-power  dissecting  lens. 

(1 )  In  the  picro-acid-fuchsin-stained  section  note  the  shape  and  size 

of  the  cord,  and  that  it  is   surrounded  by  a  thin  membrane,  the  pia 


tt 


% 

/ 

Fig.  223.— Cross  Section  of  Human  Spinal  Cord  through  the  Fifth  Lumbar  Segment.  X  10. 
( . Weigert  stain.)  (Marburg.)  a,  Anterior  median  fissure  ;  b,  posterior  septum  ;  c,  posterior 
column  ;  d,  lateral  column  ;  e,  anterior  column  ; /,  cell  groups  of  anterior  horn  ;  g,  poste- 
rior horn  ;  //,  posterior  root  fibres;  /,  Clarke's  column  and  fibres  entering  it  ;  J,  reticular 
process.  In  the  centre  of  the  figure  is  seen  the  central  canal  surrounded  by  the  central 
gelatinous  substance.  Ventral  and  dorsal  to  the  latter,  but  not  distinguishable  from  it, 
are  the  ventral  and  dorsal  gray  commissures.  The  dorsal  white  commissure  is  seen  at  J, 
while  the  thick  bundle  of  fibres  at  the  bottom  of  the  anterior  fissure  is  the  ventral  white 
commissure.  In  the  broad  head  of  the  posterior  horn  is  a  large  light  area,  the  gelatinous 
substance  of  Rolando,  between  which  and  the  surface  of  the  cord  is  the  zone  of  Lissauer. 
Note  fibres  passing  from  the  posterior  columns  into  the  gray  matter  of  the  posterior 
horns,  especially  into  the  column  of  Clarke  ;  the  grouping'of  cells  in  the  anterior  horn,  and 
the  anterior  root  fibres  passing  to  the  surface. 

mater  spinalis ;  the  anterior  median  fissure,  broad  and  shallow,  into 
which  the  pia  mater  extends;  the  posterior  median  septum  consisting 
of  neuroglia,  and  over  which  the  pia  mater  passes  without  entering. 


342  THE   ORGANS, 

The  gray  matter  is  seen  in  the  central  part  of  the  section,  stained 
red,  and  arranged  somewhat  in  the  form  of  the  letter  H.  Posteriorly 
the  gray  matter  extends  almost  to  the  surface  of  the  cord  as  the  pos- 
terior horns  or  cornua.  The  anterior  horns  are,  on  the  other  hand, 
short  and  broad,  and  do  not  approach  the  surface  of  the  cord.  Sur- 
rounding the  gray  matter  is  the  white  matter  stained  yellow.  This 
is  divided  by  the  posterior  horn  into  two  parts,  one  lying  between  the 
horn  and  the  posterior  median  septum,  the  posterior  column ;  the 
other  comprising  the  remainder  of  the  white  matter,  the  antero-lateral 
column.  This  latter  is  again  partially  divided  by  the  anterior  horn 
and  anterior  nerve  roots  into  a  lateral  column  and  an  anterior  column. 
In  the  concavity  between  the  anterior  and  posterior  horns  some  proc- 
esses of  the  gray  matter  extend  out  into  the  white  matter  where 
they  interlace  with  the  longitudinally  running  fibres  of  the  latter  to 
form  the  reticular  process . 

For  the  study  of  further  details  the  low-power  objective  should  be 
used. 

Gray  Matter.- — In  the  cross  portion  of  the  H  is  seen  the  central 
canal,  usually  obliterated  in  the  adult  and  represented  only  by  a  group 
of  epithelial  cells.  This  group  of  cells  divides  the  gray  matter  con- 
necting the  two  sides  of  the  cord  into  a  ventral  gray  commissure  and 
a  dorsal  gray  commissure.  Immediately  surrounding  the  epithelial 
cells  is  a  light  granular  area  composed  mainly  of  neuroglia  and  known 
as  the  central  gelatinous  substance.  Toward  the  surface  of  the  cord 
the  posterior  horn  expands  into  a  broad  head  or  caput,  in  which  is  an 
area  similar  in  general  appearance  to  that  surrounding  the  central 
canal,  the  gelatinous  substance  of  Rolando.  The  head  is  connected 
with  the  rest  of  the  gray  matter  by  a  narrower  neck  or  cervix.  Note 
the  interlacing  of  fibres  in  the  reticular  process ;  the  well-defined 
groups  of  large  nerve  cells  in  the  anterior  horns ;  the  fibres  which 
pass  out  from  the  anterior  horns  to  the  surface  of  the  cord,  anterior 
nerve  roots  (Fig.  223). 

White  Matter. — Note  the  general  appearance  of  the  white  mat- 
ter and  the  disposition  of  the  supporting  strands  of  neuroglia  tissue 
(stained  red).  The  neuroglia  is  seen  to  form  a  fairly  thick  layer  just 
beneath  the  pia  mater  from  which  trabecular  pass  in  among  the  fibres, 
the  broadest  strand  forming  the  posterior  median  septum.  If  the 
section  has  been  cut  through  a  posterior nerve  root,  a  strong  bundle  of 
posterior  root  fibres  can  be  seen  entering  the  white  matter  of  the  cord 


THE  NERVOUS  SYSTEM.  343 

to  the  inner  side  of  the  posterior  horn.  Just  ventral  to  the  anterior 
gray  commissure  is  a  bundle  of  transversely-running  medullated 
fibres — the  anterior  white  commissure  (Fig.  223). 

Such  finer  details  of  structure  as  are  brought  out  by  this  stain 
should  next  be  studied  with  the  high-power  objective. 

In  the  gray  matter  note  the  large  multipolar  ganglion  cells  of  the 
anterior  horn  with  their  coarsely  granular  protoplasm.  In  the  white 
matter  note  the  transversely -act  medullated  fibres  and  their  marked 
variation  in  size.  The  shrunken  axones  are  stained  red,  the  usually 
somewhat  broken  up  medullary  sheaths,  yellow.  Neuroglia  cells  are 
not  well  shown  by  this  method,  but  can  be  seen,  especially  in  the 
region  of  the  processus  reticularis,  with  their  irregular-shaped  cell 
bodies  and  darkly  stained  nuclei. 

(2)  In  the  Weigert-stained  section  the  only  element  stained  is  the 
medullary  sJieath  (Fig.  223);  consequently  the  white  matter,  which 
contains  a  much  larger  proportion  of  medullated  fibres  than  the  gray 
matter,  is  stained  more  deeply  than  the  latter.  Note  first  the  same 
general  structure  seen  in  the  preceding  section,  the  nerve  fibres,  how- 
ever, being  much  more  clearly  shown.  Note  the  central  gelatinous 
substance  and  the  gelatinous  substance  of  Rolando,  conspicuous  from 
their  lack  of  medullated  fibres.  Separating  the  gelatinous  substance 
of  Rolando  from  the  surface  of  the  cord  is  a  narrow  zone,  more  lightly 
stained  on  account  of  its  very  fine  fibres,  and  known  as  the  zone  of 
Lissaucr.  Note  the  exact  mode  of  entrance  and  distribution  within 
the  cord  of  the  posterior  root  fibres ;  the  passage  of  the  ventral  root 
fibres  to  the  surface  of  the  cord;  the  already  mentioned  anterior 
white  commissure ;  the  posterior  white  commissure,  consisting  of  a 
few  medullated  fibres  crossing  just  dorsal  to  the  posterior  gray  com- 
missure. Note  especially  the  plexus  of  fine  fibres  throughout  the  gray 
matter  and  the  general  interchange  of  fibres  between  the  gray  matter 
and  the  white  matter  (Fig.  223). 

While  the  general  structure  above  described  obtains  throughout 
the  cord,  the  size  and  shape  of  the  cord,  the  size  and  shape  of  the 
gray  matter,  and  the  relative  proportion  of  gray  matter  and  white 
matter,  vary  in  different  parts  of  the  cord,  which  must  therefore  be 
separately  considered. 

TECHNIC. 

(1)  From  a  cord  prepared  according  to  technic  1,  p.  340,  remove  small  seg- 
ments from  each  of  the  following  levels :  (1)  the  twelfth  dorsal,  (2)  the  mid-dorsal. 


344 


THE  ORGANS. 


and  (3)  the  cervical  enlargement.  The  segments  are  embedded  in  celloidin,  sec- 
tions cut  15  to  20"  thick,  stained  by  Weigert's  method  (page  25),  and  mounted  in 
balsam.  Medullated  sheaths  alone  are  stained  by  this  method  and  appear  dark 
blue  or  black. 

Practical  Study. 

Section  through  the  Twelfth  Dorsal  Segment  (Fig.  224). 

Note  that  the  cord  is  smaller  than  in  the  lumbar  enlargement  and 

somewhat  flattened  dorso-ventrally ;  that  the  amount  of  gray  matter 
and  white  matter  is  diminished ;  that  both  anterior  and  posterior 
horns  are  more  slender,  the  anterior  horn  containing  comparatively 
few  cells.     At  the  inner  side  and  base  of  the  posterior  horn  may  be 


FIG.  224.- Cross  Section  of  Human  Spinal  Cord  through  the  Twelfth  Dorsal  Segment.  X  10. 
(Weigert  stain.;  (Marburg.)  a,  Fibres  of  posterior  column  entering  Clarke's  column  ; 
/>,  fibres  passing  from  Clarke's  column  cells  to  the  direct  cerebellar  tract;  c,  Clarke's 
column. 


seen  a  small  group  of  cells  belonging  to  Clarke  s  column.  These 
cells  form  a  continuous  column  from  the  third  lumbar  to  the  seventh 
cervical  segments,  but  are  most  numerous  in  the  upper  lumbar  and 
lower  dorsal  region.  Isolated  portions  of  the  nucleus  arc  found  in 
the  sacral  and  in  the  upper  cervical  cord.  Medullated  fibres  can  be 
seen  passing  into  Clarke's  column,  where  they  interlace  among  the 
ganglion  cells. 

Section  through  the  Mid-dorsal  Region  (Fig.  225). — Com- 
pare with  the  lumbar  sections.  Note  the  change  in  shape  and  size; 
that  the  cord  is  more  nearly  round  and  smaller;  that  while  the  reduc- 
tion in  size  affects  both  gray  matter  and  white  matter,  it  is  the  former 
that  shows  the  greater  decrease.      The   horns  arc  even  more  slender 


THE  NERVOUS  SYSTEM. 


345 


than  in  the  first  lumbar  section,  and  the  anterior  horn  contains  still 
fewer  cells.     Clarke's  column  is  present,  but  not  so  large. 


FIG.  225. — Cross  Section  of  Human  Spinal  Cord  through  the  Eighth  Dorsal   Segment.     X  10. 
(Weigert  stain.)     (Marburg.)     a,  Reticular  process;  6,  Clarke's  column. 

Section  through  the  Cervical  Enlargement   (Fig.  226). — 
Note  the  marked  increase  in  size  of  the  cord,  which  affects  both  gray 


FIG.  226.— Cross  Section  of  Human  Spinal  Cord  through  Fourth  Cervical  Segment.  X  10. 
(Weigert  stain.)  (Marburg.)  Note  lateral  extension  of  anterior  horn  to  form  the  lateral 
horn,  a,  Reticular  process;  b,  Clarke's  column:  c,  septum  between  column  of  Goll  and 
column  of  Burdach. 


346  THE   ORGANS. 

matter  and  white  matter.  Depending  upon  the  exact  level  at  which 
the  section  is  taken,  the  cord  may  be  nearly  round  or  flattened  dorso- 
ventrally.  The  posterior  horns  remain  slender  while  the  anterior  are 
much  broader  and  have  lateral  extensions  known  as  the  lateral  horns. 
The  reticular  process  is  more  prominent  than  in  any  of  the  pre- 
vious sections.  As  in  the  lumbar  cord,  the  cell  groups  of  the  anterior 
horn  are  numerous  and  well  defined.  A  more  or  less  definite  septum 
divides  the  posterior  column  into  an  inner  part,  the  column  of  Goll, 
and  an  outer  part,  the  column  of  Burdach. 

Origin  of  the  Fibres  which  Make  u     the  White  Matter  of  the 

Cord. 

It  has  already  been  observed  that  the  white  matter  of  the  cord  is 
composed  mainly  of  medullated  nerve  fibres,  most  of  which  run  in  a 
longitudinal  direction.  From  our  study  of  the  neurone  it  follows 
that  each  of  these  fibres  must  be  the  axone  of  some  nerve  cell. 
These  cells,  the  axones  of  which  form  the  white  matter  of  the  cord, 
are  situated  as  follows  : 

f  (i)  Cells  outside  the  central  nervous  system  (spinal 

A.  Cells    outside    the    spinal  J  ganglion  cells). 

cord.     (Extrinsic  cells.)  \  (2)  Cells  in  other  parts  of  the  central  nervous  sys- 
[         tern  (the  brain). 

( (3)  Root  cells,  such  as  those  of  the  anterior  horn, 
whose  axones  form  the  ventral  root. 
(4)  Column  cells,  whose  axones  enter  into  forma- 

B.  Cells  situated  in  the  gray  |  tion  of  the  fibre  columns  of  the  cord, 
matter  of  the  cord.    (In-\  (5)  Cells  of  Golgi,  type  II.,  the  axones  of  which 


trinsic  cells.) 


ramify  in  the  gray  matter.  (These  cells  do  not 
give  rise  to  fibres  of  the  white  matter,  but  are 
conveniently  mentioned  here  among  the  other 
cord  cells.) 


(1)   The  Spinal  Ganglion  Cell  and  the  Origin  of  the 
Posterior  Columns. 

The  fibres  of  these  columns  consist  mainly  of  ascending  and  de- 
scending branches  of  the  fibres,  which  enter  the  cord  as  the  pos- 
terior nerve  roots.  Following  these  fibres  outward,  they  are  seen  to 
originate  in  the  cells  of  the  spinal  ganglia.  In  very  early  embry- 
onic life  the  group  of  cells  which  later  becomes  a  spinal  ganglion  is 
represented  by  a  few  cctodcrmic  cells  which  lie  between  the  closing 
medullary  plate  and  the  external  layer  of  the  ectoderm.  These  cells 
become  separated  from  the  medullary  plate  by  the  mesoderm.      At 


THE  NERVOUS   SYSTEM. 


347 


first  round,  these  cells  which  have  thus  migrated  from  the  central 
nervous  system  soon  become  spindle-shaped,  and  from  each  end  of 
the  spindle  a  process  grows  out :  one,  directed  toward  the  surface  of 
the  body,  joins  the  axones  of  the  cells  of  the  anterior  horn  to  make 
up  the  mixed  spinal  nerve;  the  other,  directed  centrally,  enters  the 
cord  as  one  of  the  fibres  of  the  posterior  root  (Fig.  227).      During  its 


FlG.  227. — Transverse  Section  through  Spinal  Cord  and  Posterior  Root  Ganglia  of  an  Embrvo 
Chick.  (Van  Gehuchten.)  a,  Spinal  ganglion,  its  bipolar  cells  sending  their  peripheral 
processes  outward  to  become  fibres  of  the  mixed  spinal  nerve  (/),  their  central  processes 
into  the  dorsal  columns  of  the  cord  as  the  dorsal  root  fibres  (6);  within  the  posterior  col- 
umns these  fibres  can  be  seen  bifurcating  and  sending  collaterals  into  the  gray  matter  of 
the  posterior  columns,  one  collateral  passing  to  the  gray  matter  of  the  opposite  side. 
The  few  efferent  fibres  of  the  dorsal  root  (c)  are  disproportionately  conspicuous.  The 
large  multipolar  cells  of  the  ventral  horns  are  seen  sending  their  axones  (i/)  out  of  the 
cord  as  the  ventral  root  fibres  (e)  which  join  the  peripheral  processes  of  the  spinal  gan- 
glion cells  to  form  the  mixed  spinal  nerve  (/);  col,  collateral  from  axone  of  ventral  horn 
cell.  Dendrites  of  the  anterior  horn  cells  are  seen  crossing  the  median  line  in  the  ante- 
rior commissure.  About  the  centre  of  the  cord  is  seen  the  central  canal ;  dorsal  and  ven- 
tral to  the  latter  some  ependymal  cells  stretching  from  the  canal  to  the  periphery  of  the 
cord. 

development  the  two  processes  of  the  bipolar  cell  approach  each 
other  and  in  the  adult  are  connected  with  the  cell  body  by  a  single 
process.  The  adult  spinal  ganglion  cell  is  thus  apparently  a  unipolar 
cell,  its  single  process  dividing  and  sending  one  arm  toward  the  per- 
iphery, the  other  toward  the  spinal  cord. 

Entirely  analogous  to  the  spinal  ganglia  are  the  ganglia  of  the 
sensory  cranial  nerves,  an  exception  to  the  unipolarity  of  the  ganglion 
cell  being  found  in  the  acoustic  ganglia,  where  in  man,  and  in  mam- 
mals generally,  the  bipolar  condition  remains  throughout  life. 

The    PERIPHERAL    ARMS    OF    THE    SPINAL    GANGLION    CELLS    make 

up  the  sensory  or  afferent  portions  of  the  spinal  nerves.      The  modes 


343 


THE   ORGAXS. 


of  termination  of  these  peripheral  processes  are  extremely  varied  and 
complicated.  These  peripheral  terminations  are  always  free,  in  the 
sense  that,  while  possibly  sometimes  penetrating  cells,  they  probably 
never  become  directly  continuous  with  their  protoplasm. 

In  the  skin,  and  in  those  mucous  membranes  which  are  covered 
with  squamous  epithelium,  the  nerve  fibres  lose  their  medullary 
sheaths  in  the  subepithelial  tissue,  and,  penetrating  the  epithelial 
layer,  split  up  into  minute  fibrils  which  pass  in  between  the  cells  and 
terminate  there,  often  in  little  knob-like  swellings  (Fig.  228).  In 
addition  to  such  comparatively  simple  nerve  endings,  there  are  also 
found  in  the  skin  and  mucous  membranes,  especially  where  sensation 
is  most  acute,  much  more  elaborate  terminations.  These  may  be 
classified  as  (i)  tactile  cells,  (2)  tactile  corpuscles,  and  (3)  end 
bulbs. 

A  simple  tactile  cell  is  a  single  epithelial  cell,  the  centrally  di- 
rected end  of  which    is  in  contact  with   a   leaf-like  expansion  of   the 


Fig.  228.— Free  Endings  of  Afferent  Nerve  Fibres  in  Epithelium  of  Rabbit's  Bladder,  (ket- 
zius.)  o,  Surface  epithelium  of  bladder;  bg,  subepithelial  connective  tissue;  n,  nerve 
fibre  entering  epithelium  where  it  breaks  up  into  numerous  terminals  amony  the  epithe- 
lial cells. 


nerve  terminal,  the  tactile  meniscus.  In  the  corpuscles  of  Grandry, 
found  in  the  skin  of  birds,  and  in  Merkel's  corpuscles,  which  occur 
in  mammalian  skin,  several  epithelial  cells  are  grouped  together  to 
receive  the  nerve  terminations.      These  are  known  as  compound  tac- 


THE  NERVOUS   SYSTEM. 


349 


tile  cells,  the  axis   cylinder  ending  in  a  flat  tactile  disc  or  discs  be- 
tween the  cells. 

Of  the  tactile  corpuscles  (Fig.  229)  those  of  Meissner,  which  occur 
in  the  skin  of  the  fingers  and  toes,  are  the  best  examples.  These 
corpuscles  lie  in  the  papillae  of  the  derma.      They  are  oval  bodies, 


Fig.  229. 


Fig.  230. 


Fig.  229.— Tactile  Corpuscle  of  Meissner,  tactile  cell  and  free  nerve  ending.  (Merkel-Henle.) 
ti,  Corpuscle  proper,  outside  of  which  is  seen  the  connective-tissue  capsule  ;  b,  fibre  end- 
ing on  tactile  cell  ;  c,  fibre  ending  freely  among  epithelial  cells. 

FIG.  230.— Taste  Bud  from  circumvallate  papilla  of  tongue.  (Merkel-Henle.)  a,  Taste  pore  ; 
b,  nerve  fibres  entering  taste  bud  and  ending  upon  neuro-epithelial  cells.  On  either  side 
fibres  ending  freely  among  epithelial  cells.     (See  also  page  448.) 

surrounded  by  a  connective-tissue  capsule  and  composed  of  flattened 
cells.  From  one  to  four  medullated  nerve  fibres  are  distributed  to 
each  corpuscle.  As  a  fibre  approaches  a  corpuscle,  its  neurilemma 
becomes  continuous  with  the  fibrous  capsule,  the  medullary  sheath 
disappears,  and  the  fibrillar  pass  in  a  spiral  manner  in  and  out  among 
the  epithelial  cells. 

Of  the  so-called  end  bulbs,  the  simplest,  which  are  found  in  the 
mucous  membrane  of  the  mouth  and  conjunctiva,  consist  of  a  central 
core  formed  by  the  usually  more  or  less  expanded  end  of  the  axis 
cylinder,  surrounded  by  a  mass  of  finely  granular,  nucleated  proto- 
plasm— the  inner  bulb — the  whole  enclosed  in  a  capsule  of  flattened 
connective-tissue  cells.  More  complicated  are  the  Pacinian  bodies 
found  in  the  subepithelial  tissues  of  the  skin  and  in  many  other 
organs  of  mammalia.     The  Pacinian  bodies  (Fig.  231)  are  laminated, 


THE   ORGANS. 


elliptical  structures  which  differ  from  the  more  simple  end  bulbs 
already  described,  mainly  in  the  greater  development  of  the  capsule. 
The  capsule  is  formed  by  a  large  number  of  concentric  lamellae,  each 
lamella  consisting  of  connective-tissue  fibres  lined  by  a  single  layer 

of  flat  connective-tissue  cells.  The 
lamellae  are  separated  from  one  another 
by  a  clear  fluid  or  semi-fluid  substance. 
As  in  the  simpler  end  bulbs  there  is  a 
cylindrical  mass  of  protoplasm  within 
the  capsule  known  as  the  inner  bulb. 
Extending  lengthwise  through  the  centre 
of  the  inner  bulb,  and  often  ending  in  a 
knob-like  extremity,  is  the  axis  cylinder 
(Fig.  231). 

In  voluntary  muscle  afferent  nerves 
terminate  in  Pacinian  corpuscles,  in  end 
bulbs,  and  in  complicated  end  organs 
called  muscle  spindles,  or  neuromuscular 
bundles.  The' muscle  spindle  (Fig.  232) 
is  an  elongated,  cylindrical  structure 
within  which  are  muscle  fibres,  connec- 
tive tissue,  blood-vessels,  and  medullated 
nerves.  The  whole  is  enclosed  in  a  con- 
nective-tissue sheath  which  is  pierced  at 
various  points  by  nerve  fibres.  A  single 
spindle  contains  several  muscle  fibres  and 
nerves.  According  to  Ruffini,  there  are 
three  modes  of  ultimate  terminations  of 
the  nerve  fibrils  within  the  spindles  :  one 
in  which  the  end  fibrils  form  a  series  of  rings  which  encircle  the  in- 
dividual muscle  fibre,  he  calls  annular  terminations;  a  second  in 
which  the  nerve  fibrils  wrap  around  the  muscle  fibres  in  a  spiral  man- 
ner— spiral  terminations ;  a  third  in  which  the  terminations  take  the 
form  of  delicate  expansions  on  the  muscle  fibre — arborescent  termina- 
tions. At  the  junction  of  muscle  and  tendon  are  found  the  elaborate 
afferent  terminal  structures  known  as  the  muscle-tendon  organs  of 
Golgi. 

In  heart  muscle  (Fig.  233)  and  in  smooth  muscle  (Fig.  234)  the 
nerves  of  the  sympathetic   system    end   in  fine  feltworks  of  fibres, 


Fig.  231. — Pacinian  Body  from 
Mesentery  of  Cat.  (Ranvier.) 
c.  Lamina  of  capsule;  d,  epithe- 
lioid cells  lying  between  lamina 
of  capsule;  «,  nerve  fibre,  con- 
sisting of  axis  cylinder  sur- 
rounded by  Henle's  sheath, 
leaving  Pacinian  body  :  f,  peri- 
neural sheath;  m,  inner  bulb; 
«,  terminal  fibre  which  breaks 
up  at  a  into  irregular  bulbous 
terminal  arborizations. 


THE  NERVOUS  SYSTEM. 


351 


which  are  in  relation  with  the  muscle  cells.  Satisfactory  differen- 
tiation between  efferent  terminals  and  afferent  terminals  in  heart  and 
in  smooth  muscle  has  not  yet  been  made. 

In  organs  whose  parenchyma  is  made  up  of   so-called  glandular 
epithelium,  the  sympathetic  nerves  terminate  mainly  in  free  endings 

F 


A 
A 


FIG.  232. — Middle  Third  of  Muscle  Spindle   from    Striated  Voluntary  Muscle  Fibre  of   Cat. 
(From  Barker,  after  Ruffini.)     A,  rings;  S,  spirals  ;  F,  dendritic  branchings. 


which  lie  in  the  cement  substance  between  the  cells,  thus  coming  in 
contact  with,  though  not  penetrating,  the  epithelial  cells. 

It  is  important  to  bear  constantly  in  mind  the  fact  that  these 
nerve  terminals,  however  complicated,  are  in  no  sense  nerve  centres 
like  the  ganglion  cells,  but  merely  more  or  less 
elaborate  end  arborizations  for  the  purpose  of 
receiving  impulses. 

Because  of  the  fact  that  it  transmits  the 
impulse  toward  its  cell  of  origin,  as  well  as  be- 
cause of  certain  other  facts,  Van  Gehuchten 
considers  this  peripheral  arm  of  the  spinal 
ganglion  cell  of  the  nature  of  a  protoplasmic 
process. 

The  Centrally  Directed'  Arm  of  the 
Spinal  Ganglion  Cell. — According  to  Van 
Gehuchten  this  represents  the  true  axone.  It 
enters  the  spinal  cord  as  one  of  the  fibres  of  the 

posterior  root,  the  entire  bundle  of  posterior  root  fibres  of  a  single 
spinal  nerve  consisting  of  all  the  central  axones  of  the  corresponding 
spinal  ganglion  (Fig.  227).  Having  entered  the  cord,  the  axone  divides 
in  the  posterior  columns  into  an  ascending  arm  and  a  descending  arm, 


[G.  233. — Nerve  Endings 
on  Heart  Muscle  Cells. 
(From  Barker,  after  Hu- 
ber  and  De  Witt.) 


352  THE   ORGANS. 

and  these  ascending  and  descending  arms  of  the  central  processes  of 
the  cells  of  the  spinal  ganglia  constitute  the  great  majority  of  the 
fibres  of  the  posterior  columns.  The  descending  arm  is  usually 
short,  sends  off  branches  known  as  collaterals  into  the  gray  matter  of 
the  cord,  and  itself  terminates  there  at  no  great  distance  below  its 
point  of  entrance  into  the  cord.      The  ascending  arm  may  behave  in 

A. 

a  I  -  "Ctai-,.,, 


Fig.  234.— Nerve   Endings    on    Smooth   Muscle   Cells.     (From  Barker,  after  Huber  and   De 
Witt.)     (/,  Axrs  cylinder  ;  b,  its  termination  ;  //,  nucleus  of  muscle  cell. 

a  similar  manner,  passing  up  the  cord  but  a  short  distance,  where, 
after  sending  collaterals  into  the  gray  matter,  it  also  terminates  in 
the  gray  matter  of  the  cord  (Fig.  237).  Instead  of  being  short  it 
may  be  of  considerable  length,  passing  some  distance  up  the  cord 
before  finally  terminating  in  the  gray  matter.  It  may,  as  one  of 
the  long  fibres  of  the  posterior  columns,  continue  into  the  medulla 
to  end  there  in  one  of  the  posterior  column  nuclei. 

(2)  Cells  Situated  in  Other  Parts  of  the  Central  Nervous 
System  which  Contribute  Axones  to  the  White  Columns 
of  the  Cord. 

The  most  important  of  these  are  the  cells  of  the  motor  area  of  the 
cerebral  cortex.  The  axones  of  these  cells  pass  down  the  cord,  form- 
ing the  direct  and  crossed  pyramidal  tracts  (page  362). 

(3)   Root  Cells — Motor  Cells  of  the  Anterior   Horn. 

These  are  large  multipolar  cells  found  at  all  levels  of  the  cord 
and  having  analogues  in  the  motor  nuclei  of  the  cranial  nerves. 
They  are  most  numerous  in  the  cervical  and  lumbar  enlargements. 
In  cross  sections  of  the  cord,  especially  through  the  enlargements, 
a  more  or  less  definite  grouping  of  these  cells  is   evident  (Figs.  223 


THE  NERVOUS  SYSTEM.  353 

and  226).  These  groups  extend  for  varying  distances  up  and  down 
the  cord,  forming  nuclei,  each  one  of  which  corresponds  to  the  inner- 
vation of  a  particular  muscle  or  group  of  muscles.  Two  columns  of 
nuclei  are  quite  constant  throughout  the  entire  length  of  the  cord. 
They  are  known,  from  the  positions  which  they  occupy,  as  the  medial 
column  and  the  intermedio-lateral  column,  and  are  related  to  the 
muscles  of  the  trunk.  At  certain  levels  these  columns  may  be 
divided  into  secondary  columns.  In  the  cervical  and  lumbar  enlarge- 
ments other  groups  of  nerve  cells  appear  which  are  concerned  in  the 
innervation  of  the  muscles  of  the  extremities.  They  are  known  re- 
spectively as  the  cell  column  of  the  upper  extremity  and  the  cell  col- 
umn  of  the  lower  extremity.  The  cell  columns  are  best  seen  in  the 
sections  from  different  levels  of  the  cord  described  on  pages  341  to 
345.  The  dendrites  of  these  cells  ramify  in  the  gray  matter,  where 
they  intermingle  with  the  terminal  ramifications  and  collaterals  of 
sensory  fibres  and  of  fibres  of  the  direct  and  crossed  pyramidal  tracts. 
Their  axones  pass  out  of  the  ventral  horn,  across  the  ventro-lateral 
column,  and  leave  the  cord  as  the  anterior,  motor,  or  efferent  roots 
of  the  spinal  nerves  (Fig.  227,  e).  The  fibres  of  this  root  pass  by  the 
spinal  ganglion  without  entering  it,  and  beyond  join  the  fibres  from 
the  ganglion  to  form  the  mixed  spinal  nerve.  On  their  way  to  the 
muscles  the  motor  axones  may  bifurcate  several  times,  thus  allowing 
one  neurone  to  innervate  more  than  one  muscle  fibre.  In  the  peri- 
mysium the  nerve  fibres  undergo  further  branching,  after  which  the 
fibres  lose  their  medullary  sheaths  and  pass  to  the  individual  muscle 
fibres.  Here  each  fibre  breaks  up  into  several  club-like  terminals 
which  constitute  the  motor  end  plate.  The  location  of  the  end  plate, 
whether  within  or  without  the  sarcolemma,  has  not  been  determined. 
As  a  rule  each  muscle  fibre  is  supplied  with  a  single  end  plate,  though 
in  large  fibres  there  may  be  several. 

These  neurones  whose  bodies  are  situated  in  the  anterior  horn 
and  whose  axones  are  the  motor  fibres  of  the  spinal  nerves,  together 
with  the  analogous  neurones  of  the  cranial  nerves  (see  page  368),  con- 
stitute the  peripheral  motor  or  efferent  neurone  system. 

(4)  Column  Cells. 

These  are  cells  which  lie  in  the  gray  matter  of  the  cord  and  send 
their  axones  into  the  white  matter  where  they  form  columns  of  nerve 
23 


354 


THE   ORGANS. 


fibres.  Some  of  the  cells  send  their  axones  into  the  white  matter  of 
the  same  side  of  the  cord.  These  are  known  as  tautomeric  cells  (Fig. 
235,  E).  Others  send  their  axones  as  fibres  of  the  anterior  commis- 
sure to  the  white  matter  of  the  opposite  side  of  the  cord — heteromeric 
cells.  In  still  others  the  axone  divides,  one  branch  going  to  the  white 
matter  of  the  same  side,  the  other  to  the  white  matter  of  the  opposite 
side — hecatcromeric  cells  (Fig.  235,  A,  B,  C). 

The  axones  of  many  of  these  cells  are  short,  constituting  the  short 
fibre  tracts  (fundamental  columns — ground  bundles)  of  the  cord  (see 


dorsal 

FlG.  235.— Cross  Section  through  .Spinal  Cord  of  Embryo  Chick  of  Eight  Days'  Incubation. 
(Kdlliker,  after  Raym6n  y  Cajalj  A,  Hecateromeric  cell  with  axone  sending  off  side 
fibril  to  gray  matter  and  then  dividing,  one  branch  passing  to  the  white  matter  of  the 
same  side,  d,  the  other  through  the  ventral  commissure  to  the  white  matter  of  the  oppo- 
site side,  a  and  d.  B  and  C",  Hecateromeric  cells  of  the  dorsal  gray  matter;  the  axones 
divided,  one  branch,  a,  passing  to  the  dorsal  while  columns  of  the  same  side,  the  other,  c, 
through  the  anterior  commissure  to  the  opposite  side  of  the  cord.  /),  Tautomeric  cell, 
tn'' axones  branching,  but  all  brandies  passing  to  the  gray  matter  or  white  matter  of  the 
same  side  of  the  cord.  /T,  Tautomeric  cell  of  the  ventral  horn  with  axone  dividing  into 
two  branches,  a  and  d,  in  the  white  matter  of  the  same  side. 


page  364);  others  are  long  (Gowers1  tract  and  the  direct  cerebellar 
tract),  passing  up  through  the  cord  and  medulla  to  higher  centres 
(see  page  361).  From  these  axones,  terminals  and  collateral  branches 
are  constantly  re-entering  the  gray  matter  to  end  in  arborizations 
around  the  nerve  cells  (Fig.  237). 


THE  NERVOUS  SYSTEM. 


355 


=  Black. 

=  Violet, 

o'  Bniuiuuiimii   =  Blue. 

e =  Brown 

f  -  =  Green. 


Flr>.  236. — Scheme  of  the  Xeurone  Relations  of  the  Spinal  Cord  ;  Nerve  Cells  shown  in  Right 
Half  of  Cord  ;  Spinal  Ganglion,  Nerve  Fibres,  and  Collaterals  shown  in  Left  Half  of  Cord. 
(From  Barker,  after  von  Lenhossek).  The  color  scheme  of  the  original  is  indicated  by 
variations  in  shading  (see  explanation  below  and  to  the  left  of  cut). 

Rig/it  Side  of  Cord. — Black-  two  motor  cells  whose  axones  after  giving  off  short  side 
fibrils  within  the  gray  matter  leave  the  cord  as  fibres  of  the  ventral  root,  R.  v.  AV</— tauto- 
meric neurones.  The  axones  of  many  of  these  cells  after  giving  off  side  fibrils  within  the 
gray  matter  are  seen  passing  to  the  ventral  and  lateral  ground  bundles  (s  and  6)  where 
they  divide  into  ascending  and  descending  arms.  Two  tautomeric  cells  are  seen  sending 
their  axones  across  the  ventral  ground  bundles  to  the  tract  of  Gowers,  j\  in  which  they 
ascend.  One  Clarke's  column  cell  is  represented  sending  its  axone  across  the  intervening 
white  matter  to  ascend  in  the  direct  cerebellar  tract,  4.  Violet — heteromeric  neurones, 
the  axones  of  which  pass,  some  to  the  gray  matter,  others  to  the  white  matter  of  the 
opposite  side  of  the  cord.  From  the  latter  are  given  off  collaterals  to  the  gray  matter. 
Green—  tautomeric  neurones  whose  axones  pass  to  the  dorsal  columns.  Blue—  Golgi  cell 
Type  II.,  the  axone  of  which  ramifies  in  the  gray  matter  in  the  vicinity  of  its  cell  of  origin. 

Left  Side  of  Cord.  —  Black  Cells,  G.s.  —  spinal  ganglion  cells.  The  single  process  bifur- 
cates, the  peripheral  arm  becoming  a  fibre  of  the  dorsal  root,  R.d.,  the  central  arm  enter- 
ing the  dorsal  column  where  it  divides  into  a  short  descending  and  a  longer  ascending 
arm.  From  both  ascending  and  descending  arms  collaterals  are  seen  passing  into  the 
gray  matter  and  terminating  in  arborizations  in  the  posterior  horn,  in  the  anterior  horn 
and  in  Clarke's  column.  One  collateral  is  seen  crossing  through  the  posterior  commis- 
sure to  the  gray  matter  of  the  opposite  side.  The  red  fibres  (indicated  by  continuous 
black  lines)  are  collaterals  and  terminals  from  the  direct  cerebellar  tract,  from  the  tract 
of  Gowers,  and  from  the  lateral  and  ventral  ground  bundles,  passing  to  their  termina- 
tions in  the  gray  matter.  The  brown  fibres  (indicated  by  dotted  lines)  are  collaterals  and 
terminals  from  the  direct  and  crossed  pyramidal  tracts  which  are  seen  terminating  in 
the  gray  matter  of  the  anterior  horn. 

/,  Direct  pyramidal  tract ;  2.  ventral  ground  bundle  ;  j,  tract  of  Gowers  :  j,  direct  cere- 
bellar tract  ;  j,  crossed  pyramidal  tract;  6.  lateral  ground  bundles;  7,  dorsal  columns; 
R.v.,  ventral  root  ;  R.d.,  dorsal  root;  G.s.,  spinal  ganglion. 


356,  THE   ORGANS 

(5)   Cells  of  Golgi  Type  II. 

The  axones  of  these  cells  do  not  leave  the  gray  matter,  but  divide 
rapidly  and  terminate  in  the  gray  matter  near  their  cells  of  origin, 
some  crossing  to  terminate  in  the  gray  matter  of  the  opposite  side 
(Fig.  236). 

TECHNIC. 

(1)  For  the  purpose  of  studying  the  spinal  ganglion  cell  with  its  processes  and 
their  relations  to  the  peripheral  nerves  and  to  the  cord,  the  most  satisfactory  mate- 
rial is  the  embryo  chick  of  six  days"  incubation,  treated  by  the  rapid  silver  method 
of  Golgi  (technic  b,  p.  27).  Rather  thick  (75/')  transverse  and  longitudinal  sec- 
tions are  made  and  mounted  in  hard  balsam  without  a  cover-glass.  Owing  to  the 
uncertainty  of  the  Golgi  reaction  several  attempts  are  frequently  necessary  before 
good  sections  are  obtained. 

(2)  The  root  cells  of  the  anterior  horn  with  their  axones  passing  out  of  the 
cord  and  joining  the  peripheral  processes  of  the  spinal  ganglion  cells,  to  form  the 
spinal  nerves,  can  usually  be  seen  in  the  transverse  sections  of  the  six-day  embryo 
chick  cord  prepared  as  above,  technic  (1). 

(3)  For  studying  the  column  cells  of  the  cord,  embryo  chicks  of  from  rive  to  six 
days'  incubation  should  be  treated  as  in  technic  (1 ).  Owing  to  the  already  mentioned 
uncertainty  of  the  Golgi  reaction,  it  is  usually  necessary  to  make  a  large  number  of 
sections,  mounting  only  those  which  are  satisfactorily  impregnated.  It  is  rare  for 
a  single  section  to  show  all  types  of  cells.  Some  sections  contain  tautomeric  cells, 
some  contain  heteromeric,  while  in  very  few  will  the  hecateromeric  type  be  found. 

Sections  containing  fewest  impregnated  cells  frequently  show  collaterals  to 
best  advantage.  These  are  seen  as  a  fringe  of  tine  fibres  crossing  the  boundary 
line  between  gray  matter  and  white  matter. 

Practical  Study. 

Transverse  Section  of  Six-day  Chick  Embryo  (Technic  1). 
— Using  a  low-power  objective,  first  locate  the  cord  and  determine 
the  outlines  of  gray  matter  and  white  matter.  Observe  the  spinal 
ganglia  lying  one  on  either  side  of  the  cord  (Fig.  227,  a).  One  of  the 
ganglia  will  probably  show  one  or  more  bipolar  cells,  sending  one 
process  toward  the  periphery,  the  other  toward  the  spinal  cord.  Note 
that  the  peripheral  process  is  joined,  beyond  the  ganglion,  by  fibres 
which  come  from  the  ventral  region  of  the  cord  (fibres  of  the  anterior 
root).  In  some  specimens  the  latter  can  be  traced  to  their  origin  in 
the  cells  of  the  anterior  horn  (Fig.  227,  d).  The  union  of  the  periph- 
eral processes  of  the  spinal  ganglion  cells  and  the  anterior  horn  fibres 
is  seen  to  make  up  the  mixed  spinal  nerve  (Fig.  227,7").  Observe 
the  central  processes  of  the  spinal  ganglion  cells  entering  the  dorsal 


THE  NERVOUS   SYSTEM. 


357 


column  of  the  cord  and  bifurcating  (Fig.  227,  b).  As  these  branches 
pass  up  and  down  the  cord,  only  a  short  portion  of  each  can  be  seen  in 
a  transverse  section.  Note  the  fibres 
(collaterals)  passing  from  the  white 
matter  into  the  gray  matter.  Note  in 
some  of  the  sections,  a  little  round 
mass  just  ventral  and  to  the  inner  side 
of  the  spinal  ganglion,  in  which  nerve 
cells  may  be  seen,  and  some  fibres 
passing  into  or  out  of  it.  This  rep- 
resents the  beginning  of  the  sympa- 
thetic system  with  its  chain  of  gan- 
glia. Note  the  relation  which  this 
bears  to  the  spinal  cord  and  spinal 
ganglia. 

Longitudinal  Section  of  Six- 
day  Chick  Embryo  (Technic  1,  p. 
356).- — Using  a  low-power  objective 
locate  gray  matter  and  white  matter 
and  identify  plane  of  section  relative 
to  transverse  section  above  described. 
Note  in  the  white  matter  longitudinal- 
ly-running fibres  from  which  branches 
pass  off  into  the  gray  matter  (Fig.  237). 
Those  of  the  posterior  columns  are  the 
ascending  and  descending  branches  of 
the  central  processes  of  the  spinal  gan- 
glion cells,  and  the  branches  passing 
into  the  gray  matter  are  their  collater- 
als and  terminals.  If  the  section  hap- 
pens to  include  the  entering  fibres  of  a 
posterior  root,  these  can  be  seen  branch- 
ing in  the  posterior  columns  into  as- 
cending and  descending  arms  (Fig. 
237).  The  longitudinal  fibres  of  the 
lateral  and  anterior  columns  are  ax- 
ones  of  column  cells  and  of  cells  sit- 
uated in  higher  centres  (see  pages  352  and  353) 
collaterals  and  terminals  into  the  gray  matter. 


Fig.  237.— From  Longitudinal  Section 
of  Spinal  Cord  of  Embryo  Chick. 
(Van  Gehuchten.)  A,  White  columns 
of  cord  ;  B,  gray  matter.  The  cells 
of  the  gray  matter  (column  cells)  are 
seen  sending  their  axones  into  the 
white  matter,  where  they  bifurcate, 
their  ascending  and  descending  arms 
becoming  fibres  of  the  white  columns. 
The  dendrites  of  these  cells  are  seen 
ramifying  in  the  gray  matter.  To 
the  left  are  seen  fibres  (posterior  root 
fibres)  entering  the  white  matter  and 
bifurcating,  the  ascending  and  de- 
scending arms  becoming  fibres  of  the 
white  columns.  From  the  latter  are 
seen  fibres  ("collaterals)  passing  into 
the  gray  matter  and  ending  in  arbori- 
zations. 


These  also  send 


35! 


THE   ORGANS. 


Fibre  Tracts  of  the  Cord. 

The  fact  that  the  cell  bodies  of  neurones  are  located  in  the  gray 
matter  of  the  brain  and  spinal  cord,  in  the  ganglia,  and  in  the  per- 
ipheral end  organs  of  certain  of  the  nerves  of  special  sense,  has  been 
already  referred  to.  In  the  brain  and  cord  there  are  more  or  less 
definite  groupings  of  these  neurones  for  physiological  purposes,  their 
cell  bodies  being  grouped  together  to  form  centres  or  nuclei;  their 
axones,  following   certain    definite    paths,   known  as  fibre    tracts    or 


FIG.  238. -Diagram  showing  Fibre  Tracts  of  the  Cord,  Ascending  Tracts  being  shown  on  the 
Right  Side,  Descending  Tracts  on  the  Left  Side.  (Schafer.)  /,  Crossed  pyramidal  tract; 
2,  direct  pyramidal  tract  ;  _?,  antero-lateral  descending  tract  or  tract  of  Loewenthal  ; .?,/, 
bundle  of  Helweg  ;  7,  rubro-spinal  tract  or  von  Monakow's  bundle;  3,  comma  tract;  6, 
column  of  Coll  ;  7,  column  of  Burdach ;  S,  column  or  zone  of  Lissauer  ;  sm,  septo-mar- 
ginal  tract;  s.p.l.,  dorsal  root  zone  of  Flechsig ;  9,  direct  cerebellar  tract;  to,  tract  of 
Gowers;  a,  a1,  a*, a3,  a*,  aB,  groups  of  cells  in  the  ventral  horn;  ?',  intermedio-lateral 
group  of  cells  ;  />,  cells  of  ihe  posterior  horn  ;  </,  column  of  Clarke. 


fibre  systems.  If  the  cell  bodies  and  dendrites  be  included  with  the 
axones,  the  whole  is  known  as  a  neurone  system  ;  while  if  several 
neurone  systems  are  concerned  in  the  transmission  of  a  particular  set 
of  impulses,  the  whole  is  referred  to  as  a  conduction  path.  For  ex- 
ample, that  system  of  neurones  whose  cell  bodies  are  situated  in  the 
anterior  horns  and  whose  axones  constitute  the  motor  part  of  the 
spinal  nerves  is  known  as  the  spi  no-peripheral  neurone  system.  If 
wo  include  with  this  that  system  of  neurones  the  cell  bodies  of  which 
are  located  in  the  motor  cortex  and  the  axones  of  which  terminate 
around  the  anterior  horn  cells  of  the  cord,  the  whole  constitutes  the 
motor  cortico-spi no-peripheral  conduction  path. 


THE  NERVOUS   SYSTEM.  359 

A  nucleus  which  contains  the  cell  bodies  of  a  system  of  neurones 
is  known  as  the  nucleus  of  origin  of  that  system.  Thus  the  already 
referred  to  groups  of  cells  in  the  anterior  horns  are  the  nuclei  of  ori- 
gin for  the  spino-peripheral  neurone  system.  A  nucleus  in  which 
terminate  the  axones  of  a  system  of  neurones  is  known  as  the  termi- 
nal nucleus  oi  that  system.1  Thus  the  dorsal  nucleus,  or  Clarke's 
column,  serves  as  a  terminal  nucleus  for  some  of  the  axones  of  the 
peripheral  sensory  neurone  system  (see  page  361).  In  most  cases  a 
nucleus  is  the  terminal  nucleus  for  the  axones  of  one  neurone  system 
and  at  the  same  time  the  nucleus  of  origin  for  the  axones  of  another 
neurone  system.  Thus,  in  the  case  above  cited  the  dorsal  nucleus, 
while  serving  as  the  nucleus  of  termination  for  some  of  the  fibres  of 
the  peripheral  sensory  neurone  system,  also  serves  as  the  nucleus  of 
origin  for  a  second  neurone  system  the  axones  of  which  pass  upward 
to  higher  centres. 

The  fibre  tracts  of  the  cord  are  not  separated  from  one  another  by 
connective  tissue,  nor  do  the  fibres  of  one  tract  necessarily  differ  in 
appearance  from  the  fibres  of  other  tracts,  so  that  it  is  impossible 
morphologically  to  differentiate,  or  mechanically  to  trace  the  different 
fibre  systems  of  the  cord.  Certain  methods  of  investigation,  how- 
ever, have  enabled  us  to  determine  most  of  these  tracts  and  the  paths 
which  their  fibres  follow.  Among  the  most  important  of  these  may 
be  mentioned  the  method  of  embryology  and  the  method  of  patJiology. 
The  embryological  method  is  based  upon  the  fact  that  the  fibres  of 
different  systems  acquire  their  medullary  sheaths  at  different  periods 
of  embryonic  development.  Thus,  by  examining  cords  from  embryos 
of  different  ages,  it  is  possible  to  distinguish  the  different  tracts  by 
the  extent  of  the  myelinization  of  their  fibres.  The  pathological 
method  is  based  upon  the  fact  that  when  an  axone  is  cut  off  from 
its  cell  of  origin  it  dies  and  is  replaced  by  new  connective  tissue. 
Thus,  if  in  any  way  a  tract  of  fibres  is  interrupted,  all  of  the  axones 
of  cells  which  are  situated  on  the  other  side  of  the  lesion  atrophy  and 
can  be  traced  among  the  normal  fibres.  Advantage  is  taken  of  this 
latter  method  for  the  purpose  of  experimental  research  in  animals. 

1  The  words  "  terminal  "  and  "  terminate  "  as  here  used  refer  to  the  terminations 
of  the  axones  as  such,  and  do  not  necessarily  indicate  terminations  of  their  com- 
ponent neurofibrils  (see  page  1 1 1 ). 


360  THE  ORGANS. 

Ascending  Fibre  Tracts  of  the  Cord. 

I.  The  Posterior  Columns. — The  origin  of  these  tracts — central 
processes  of  the  cells  of  the  spinal  ganglia — has  been  described  (page 
351).  The  distribution  of  the  posterior  root  fibres  within  the  cord 
was  noted  in  connection  with  the  study  of  the  last  dorsal  and  lumbar 
enlargement  sections  (pages  341  and  344). 

Just  after  entering  the  cord  the  most  lateral  of  the  posterior  root 
fibres  turn  outward  and,  after  bifurcating,  ascend  and  descend  as  a 
tract  of  fine  fibres  which  lies  between  the  tip  of  the  posterior  horn 
and  the  surface  of  the  cord,  and  is  known  as  the  tract  or  marginal 
zone  of  Lissauer  (Fig.  238,  8).  The  rest  of  the  fibres  also  bifurcate 
and  send  their  processes  up  and  down  in  the  lateral  part  of  the  pos- 
terior column.  Each  successive  dorsal  root  sends  its  fibres  into  the 
cord  to  the  outer  side  of  those  from  the  next  root  below.  Thus  the 
fibres  of  the  lower  roots  as  they  ascend  the  cord  are  gradually  pushed 
inward  toward  the  median  line  until  they  finally  occupy  that  part  of 
the  posterior  column  lying  near  the  posterior  septum.  The  sepa- 
ration of  the  posterior  column  by  a  connective-tissue  septum  into  the 
column  of  Goll  and  the  column  of  Burdach  occurs  only  in  the  cervical 
cord  (Figs.  226  and  238).  Here  the  most  median  fibres  of  the  col- 
umn of  Goll  (Fig.  238,  6)  are  the  longest  fibres  of  the  posterior  col- 
umns, having  come  from  the  lower  spinal  ganglia,  while  the  column 
of  Burdach  (Fig.  238,  /)  consists  of  short  and  medium  length  fibres. 
Most  of  the  fibres  of  Coil's  column  end  in  the  nucleus  funiculi  gracilis 
or  nucleus  of  the  column  of  Goll  in  the  medulla  (see  p.  373,  Fig. 
243,  N.G).  Some  few  fibres  probably  pass  this  nucleus  and  are  con- 
tinued through  the  restiform  body  to  the  cerebellum.  Most  of  the 
fibres  of  Burdach's  column  terminate  in  the  medulla  in  the  nucleus 
funiculi  cuneati  or  nucleus  of  the  column  of  Burdach  (p.  373,  Fig. 
243,  N.B).  A  few  fibres  probably  pass  the  nucleus,  as  do  some  of 
those  of  the  column  of  Goll,  to  enter  the  restiform  body  and  termi- 
nate in  the  cerebellum.  The  nucleus  gracilis  and  nucleus  cuneatus 
—which  will  be  seen  in  sections  of  the  medulla  (page  373)- — thus 
serve  as  terminal  nuclei  for  most  of  the  axones  of  the  columns  of 
Goll  and  of  Burdach. 

Only  a  portion  of  the  posterior  root  fibres  pursue  the  long  course 
above  described.  From  the  posterior  columns  axones  and  collaterals 
are  constantly  passing   into  the  gray  matter  to  end   in  arborizations 


THE  NERVOUS  SYSTEM.  361 

among  the  cells  (Fig.  237).  The  gray  matter  of  the  cord  thus  serves 
as  an  extended  nucleus  of  termination  for  these  fibres.  After  enter- 
ing the  gray  matter  the  fibres  are  distributed  :  (a)  To  the  dorsal  and 
middle  region  of  the  gray  matter ;  (/>)  to  the  nucleus  dorsalis  or  col- 
umn of  Clarke ;  (c)  to  the  gray  matter  of  the  ventral  horns,  where 
they  end  around  the  motor  cells ;  (d)  through  the  posterior  commis- 
sure to  the  gray  matter  of  the  opposite  side  (Fig.  236). 

The  neurones  above  described  whose  cell  bodies  lie  in  the  spinal 
(and  cranial — see  medulla)  ganglia,  whose  peripheral  processes  with 
their  end  organs  constitute  the  receptive  apparatus,  and  whose  cen- 
tral processes  terminate  in  the  gray  matter  of  the  cord  and  medulla, 
constitute  the  peripheral  sensory  or  afferent  neurone  system. 

II.  The  Direct  Cerebellar  Tract  {Dorso- lateral  Ascending  Tract 
— Dorso- lateral  Spino- cerebellar  Fasciculus- — Tract  oj  Flcchsig). — 
This  tract  lies  along  the  dorso-lateral  periphery  of  the  cord,  being 
bounded  internally  by  the  crossed  pyramidal  tract  (Fig.  236,  4,  and 
Fig.  238,  o).  The  fibres  of  the  direct  cerebellar  tract  are  the  axones 
of  the  cells  of  Clarke's  column  (p.  355,  Fig.  236).  These  axones 
cross  the  intervening  gray  matter  and  white  matter  of  the  same  side 
(tautomeric  cells)  (Fig.  236)  and  turn  upward  as  the  direct,  cerebellar 
tract.  In  the  medulla  they  pass  into  the  restiform  body  or  inferior 
cerebellar  peduncle  and  thence  to  the  cerebellum.  Here  they  enter 
the  gray  matter  of  the  vermis  of  the  same  or  opposite  side,  ending  in 
ramifications  among  the  nerve  cells.  Some  fibres  either  end  in,  or 
send  off  collaterals  to,  the  cerebellar  nuclei.  The  tract  first  appears 
in  the  upper  lumbar  cord,  and  increases  in  size  until  the  upper  limit 
of  Clarke's  column  has  been  reached  (page  344). 

As  already  noted  above,  some  fibres  of  the  posterior  root  (cen- 
tral processes  of  spinal  ganglion  cells),  or  their  collaterals,  end  in  the 
column  of  Clarke.  The  neurones  whose  cell  bodies  form  Clarke's 
column,  and  whose  axones  constitute  the  direct  cerebellar  tract,  are 
therefore  a  second  neurone  system  in  the  sensory  conduction  path. 

III.  Gowers'  Tract  {Antero- lateral  Ascending  Tract — Fascicu- 
lus Ventro-lateralis  Superficial  is). — This  tract  lies  along  the  per- 
iphery of  the  cord,  extending  from  the  anterior  limit  of  the  direct 
cerebellar  to  the  exit  of  the  ventral  roots  (Fig.  236,  3,  and  Fig. 
238,  10).  It  is  formed  by  axones  of  neurones  whose  cell  bodies  are 
scattered  through  the  central  gray  matter  without  any  distinct  group- 
ing (Fig.    22,6).      Some  fibres    come  from    tautomeric,   others  from 


362  THE   ORGANS. 

heteromeric  cells.  The  tract  first  appears  in  the  upper  lumbar  cord 
and  naturally  increases  in  size  as  it  passes  upward.  It  appears  to  be 
formed  partly  of  spinal  association  fibres,  partly  of  fibres  which  pass 
to  higher  centres.  The  exact  paths  which  these  fibres  take  after 
leaving  the  cord  and  their  terminations  are  not  positively  determined. 
Some  of  them  end  in  the  cerebellum,  others  have  been  described  as 
ending  in  the  corpora  quadrigemina,  in  the  thalamus,  in  the  substan- 
tia nigra,  and  in  the  nucleus  lentiformis.  It  seems  probable  that 
these  varying  results  of  investigation  are  due  to  the  fact  that  the 
tract  of  Gowers  does  not  represent  a  single  physiologically  distinct 
system,  but  is  composed  of  fibres  having  several  different  functions 
and  destinations. 

Descending  Fibre  Tracts  of  the  Cord. 

I.  The  Pyramidal  Tracts. — (i)  The  Crossed  Pyramidal  Tract. 
— This  is  a  large  tract  of  fibres  lying  in  the  dorsal  part  of  the  lateral 
column  (Fig.  236,5/  Fig.  238,  /).  It  extends  to  the  lowermost 
part  of  the  cord.  In  the  cervical  and  dorsal  regions  it  is  separated 
from  the  surface  of  the  cord  by  the  direct  cerebellar  tract.  In  the 
lumbar  region  the  latter  tract  is  no  longer  present  and  the  crossed 
pyramidal  comes  to  the  surface. 

(2)  The  direct  pyramidal  tract,  or  tract  of  Tiirck,  occupies  a  small 
oval  area  adjacent  to  the  anterior  median  fissure  (Fig.  236,  /;  Fig. 
238,  2).  It  decreases  in  size  as  the  lower  levels  of  the  cord 
are  reached,  to  disappear  entirely  in  the  middle  or  lower  dorsal 
region. 

The  pyramidal  tracts  vary  greatly  in  size  in  different  individuals 
and  are  apt  to  be  asymmetrical,  this  being  due  to  the  lack  of  uni- 
formity as  to  the  number  of  fibres  which  cross  over  in  the  pyramidal 
decussation  (see  page  363). 

These  two  tracts  constitute  the  main  motor  or  efferent  fibre- 
system  of  the  cord.  The  cell  bodies  of  the  neurones  whose  axones 
make  up  this  system  are  situated  in  the  cerebral  cortex  near  the  fis- 
sure of  Rolando.  Their  axones  converge  and  pass  downward  through 
the  internal  capsule,  crura  cerebri,  pons,  and  medulla,  sending  off 
fibres  to  the  motor  nuclei  of  the  cranial  nerves.  In  the  medulla  the 
tracts  come  to  the  surface  as  the  anterior  pyramids.  At  the  junction 
of  medulla  and  cord  occurs  what  is  known  as  the  pyramidal  decus- 


THE  NERVOUS   SYSTEM.  363 

sation  (Fig.  241).  Here  most  of  the  fibres  of  each  tract  cross  to  the 
opposite  dorso- lateral  region  of  the  cord  and  continue  downward  as  the 
crossed  pyramidal  tract.  The  minority  of  the  fibres,  instead  of  de- 
cussating, remain  on  the  same  side  to  pass  down  the  cord  along  the 
anterior  median  fissure  as  the  direct  pyramidal  tract.  As  these 
tracts  descend  they  decrease  in  size  from  loss  of  fibres  which  con- 
tinually leave  them  to  terminate  in  the  ventral  horns.  The  fibres  of 
the  crossed  tract  terminate  mainly  in  the  horn  of  the  same  side, 
while  most  of  the  fibres  of  the  direct  tract  cross  through  the  an- 
terior commissure  to  the  opposite  side  of  the  cord.  These  tracts 
are  thus  mainly  crossed  tracts,  as  the  great  majority  of  their  fibres 
cross  to  the  opposite  side  of  the  cord.  The  tracts  are  apt  to  differ  in 
size  on  the  two  sides  of  the  cord,  owing  to  the  fact  that  the  propor- 
tion of  fibres  which  decussate  is  not  constant.  The  axones  termi- 
nate in  arborizations  around  the  motor  cells  of  the  ventral  horns, 
thus  constituting  the  corticospinal  motor  neurone  system.  It  will 
be  remembered  that  the  neurones  whose  cell  bodies  are  situated  in 
the  ventral  horns  constitute  the  spino-pcripheral  motor  neurone  sys- 
tem. The  two  systems  taken  together  form  the  cortico-spino-per- 
ipheral  motor  conduction  path. 

II.  The  Antero-lateral  Descending  Tract.  {Anterior  Marginal 
Bundle  of  Locivcnthal.) — This  consists  of  descending  axones  of 
neurones  whose  cell  bodies  are  situated  in  the  cerebellum.  In  the 
cord  these  fibres  lie  along  the  ventral  margin,  overlapping  the  tract 
of  Gowers  (Fig.  238,  J).  Investigators  are  not  in  accord  as  to  the 
exact  paths  which  these  fibres  follow  in  passing  from  the  cerebellum 
to  the  cord. 

III.  Von  Monakow's  Tract.  {Rubro-spinal  Tract) — This  con- 
sists of  axones  of  cells  situated  in  the  red  nucleus  of  the  opposite 
side.  In  the  cord  the  tract  lies  in  the  lateral  column  just  ventral  to 
the  crossed  pyramidal  tract  (Fig.  238,  p). 

IV.  Helweg's  tract  is  a  small  triangular  bundle  of  fibres  lying 
along  the  ventro-lateral  margin  of  the  cord,  and  is  traceable  upward 
as  far  as  the  olives  (Fig.  238,  J  a).  The  origin  and  destination  of 
its  fibres  are  not  definitely  known. 

V.  The  Septo-marginal  Tract.  {Oval  Bundle  of  Flechsig.)— 
This  is  a  small  bundle  of  fibres  lying  next  the  posterior  septum  (Fig. 
238,  sm).  It  is  probably  composed  of  descending  axones  of  cells  in 
the  cord. 


364  THE   ORGANS. 

VI.  The  so-called  "comma"  tract  of  Schultze  is  a  small 
comma-shaped  bundle  of  descending  fibres  lying  about  the  middle  of 
the  posterior  column  (Fig.  238,5).  It  is  most  prominent  in  the  dor- 
sal cord.  Its  fibres  are  believed  by  some  to  be  descending  branches 
of  spinal  ganglion  cells,  by  others  to  be  descending  axones  from  cells 
situated  in  the  gray  matter  of  the  cord  (column  cells). 

Fundamental  Columns  or  Ground  Bundles  of  the  Cord. 

The  ascending  and  descending  tracts  above  described  are  known 
as  the  long  fibre  tracts  of  the  cord.  If  the  area  which  these  tracts 
occupy  be  subtracted  from  the  total  area  of  white  matter  it  is  seen 
that  a  considerable  area  still  remains  unaccounted  for.  This  area  is 
especially  large  in  the  antero-lateral  region,  and  extends  up  along  the 
lateral  side  of  the  posterior  horn  between  the  latter  and  the  crossed 
pyramidal  tract  (Figs.  236  and  238).  A  small  area  in  the  posterior 
column  just  dorsal  to  the  posterior  commissure,  and  extending  up  a 
short  distance  along  the  medial  aspect  of  the  horn,  should  also  be 
included.  These  areas  are  occupied  by  the  fundamental  columns  or 
short-fibre  systems  of  the  cord.  The  fibres  serve  as  longitudinal 
commissural  fibres  to  bring  the  different  segments  of  the  cord  into 
communication  (Fig.  237).  The  shorter  fibres  lie  nearest  the  gray 
matter  and  link  together  adjacent  segments.  The  longer  fibres  lie 
farther  from  the  gray  matter  and  continue  through  several  segments. 
The  origin  of  these  fibres  as  axones  of  cells  of  the  gray  matter,  and 
the  manner  in  which  they  re-enter  the  gray  matter  as  terminals  and 
collaterals  have  been  considered  (page  354.) 


From  the  neurones  thus  far  studied  and  the  tracts  which  their 
axones  follow,  we  may  determine  the  following  general  impulse  path- 
wax' s  in  the  cord  : 

(1)  The  Direct  Reflex  rath  (Fig.  239). — (a)  The  peripheral  sen- 
sory neurone  ;  its  peripheral  process  and  end  organ,  the  spinal  gan- 
glion cell,  its  centra]  process  with  collaterals  terminating  around  motor 
cells  of  anterior  horn  ;  {/>)  the  peripheral  motor  neurone  ;  motor  cell 
of  anterior  horn  with  axone  passing  to  muscles,  etc.  This  is  a  two- 
neurone  reflex  path,  chiefly  uncrossed,  and  in  most  cases  involving 
only  closely  adjacent  segments. 


THE  NERVOUS   SYSTEM. 


365 


(2)  The  Indirect  Reflex  Path  (Fig.  240). — {a)  The  peripheral 
sensory  neurone  as  in  the  direct  reflex,  but  terminating  around  col- 
umn cells  of  the  cord,  (b)  The  cord  neurone  (column  cells) — axones 
forming  fundamental  columns  with  collaterals  and  terminals  to  ante- 
rior horn  cells  of  different  levels.  (c)  The  peripheral  motor  neurone 
as  in  the  direct  reflex.  This  is  a  three-neurone  reflex  path  involving 
both  sides  of  the  cord  and  segments  above  and  below  the  segment  of 
entrance  of  the  stimulus. 

(3)  Direct  Ascending-  Paths  to  Higher  Centres. — The  peripheral 
sensory  neurone  as  in  the  direct  reflex,  but  with  central  process  pass- 
ing as  fibre  of  Goll  or  Burdach  to  the  nucleus  of  one  of  these  columns 
in  medulla  (Fig.  242). 

(4)  Indirect  Ascending  Paths  to  Higher  Centres. — (a)  Peripheral 
sensory  neurone  as   in   direct  reflex,  but  communicating  in  cord  with 


FlG.  239. — Diagram  Illustrating  Path  followed  by  and  Neurones  involved  in  a  Simple  Direct 
Reflex.  (Van  Gehuchlen  )  A,  Sensory  surface  ;  B,  muscle  ;  C,  spinal  cord.  Arrows  show 
direction  of  impulse,  which  starts  at  the  sensory  surface,  passes  along  first  the  peripheral 
then  the  central  arm  of  the  spinal  ganglion  cell  to  the  dorsal  columns  of  the  cord,  thence 
by  means  of  a  collateral  or  terminal  to  the  ventral  horn,  where  it  is  transferred  to  a 
motor  cell.  The  impulse  then  passes  along  the  axone  of  the  motor  cell  (motor  fibre  of 
spinal  nerve")  to  the  muscle.  The  two  neurones  involved  in  a  simple  reflex  are  thus  seen 
to  be  the  peripheral  sensory  neurone  and  the  peripheral  motor  neurone. 

column  cells  of  direct  cerebellar  and  of  Gowers'  tracts.  (/>)  Column 
cells  sending  their  axones  to  higher  centres  in  the  direct  cerebellar 
and  Gowers'  tracts  (Fig.  361 ). 

(5)  Descending  Paths  from    Higher    Centres. — (a)  The   cortico- 


366 


THE   ORGANS. 


spinal  motor  neurone  whose  cell  bodies  are  situated  in  the  motor  cor- 
tex, and  whose  axones  form  the  pyramidal  tracts.  These  axones 
terminate  around  anterior  horn  cells,  those  of  the  crossed  tract  in  the 


FIG.  240.  —  Diagram  Illustrating  Pathway  of  Compound  Keflex  (Van  Gehuchteti)  Involving 
Three  Neurones.  /,  Peripheral  sensory  neurone  by  means  of  which  the  impulse  passes 
from  the  sensory  surface  to  the  gray  matter  of  the  cord,  as  in  Fig.  239.  In  the  gray  mat- 
ter, instead  of  passing  directly  to  a  motor  cell  as  in  the  direct  reflex,  the  impulse  is 
transferred  to  a  neurone,  2,  whose  axone  becomes  a  fibre  to  the  ground  bundles.  From 
the  latter  terminals  and  collaterals  enter  the  gray  matter  and  end  around  cells  of  the 
ventral  horn,  whence  the  impulse  is  carried  to  the  muscle  as  in  the  direct  reflex,  3.  The 
essential  difference  between  the  simple  and  the  compound  reflex  is  thus  seen  to  be  the 
interposition  of  a  third  neurone  and  the  fact  that  a  number  of  motor  cells  situated  at 
different  levels  are  involved. 

horn  of  the  same  side,  those  of  the  direct  tract  in  the  horn  of  the  op- 
posite side.  (/>)  The  peripheral  motor  neurone- — anterior  horn  cell — 
its  axone  to  muscle  (Fig.  239). 

In  addition  to  the  main  descending  paths  are  the  other  descending 
paths  mentioned  on  page  363,  by  which  an  impulse  may  pass  from 
higher  centres  to  the  cord. 

TECHNIC. 

ii)  A  human  cord  from  a  case  in  which  death  has  occurred  some  lime  after 
fracture  of  the  vertebrae  with  resulting  crushing  of  the  cord,  furnishes  valuable  but 
oi  course  rarely  available  material.  If  death  occur  within  a  few  weeks  after  the 
injury,  the  method  of  Marchi  '  should  be  used  ;  if  after  several  weeks  the  method  of 
Weigerl  (page  25).  Thepicturein  (he  cord  isdependent  upon  the  fact  that  axones 
1  hi  rill  from  their  cells  of  origin  degenerate  and  are  finally  replaced  by  connective 
tissue.  After  a  complete  transverse  lesion  of  the  cord,  therefore,  all  ascending 
tra<  is  are  found  degenerated  above  the  lesion,  all  descending  tracts  below  the  le- 

1  Marchi's  solution  consists  of  two  parts  M tiller  fluid  and  one  pari  one-per- 
cent aqueous  solution  osmic  acid.  /Alter  hardening  for  from  seven  to  ten  days  in 
Muller's  fluid,  thin  slices  of  tissue  are  transferred  to  the  Marchi  solution,  where 

"they  remain   lor   alinut    the   same    length    of    time.      Sections  are   usually  mounted 

without  further  staining:,  in  balsam. 


THE  NERVOUS  SYSTEM.  367 

sion.  The  method  of  Marchi  gives  a  positive  picture  of  osmic-acid-stained  degene- 
rated myelin  in  the  affected  tracts.  The  method  of  Weigert  gives  a  negative  pict- 
ure, the  connective  tissue  which  has  replaced  the  degenerated  tracts  being 
unstained  in  contrast  with  the  norma!  tracts,  the  myelin  sheaths  of  whose  fibres 
stain,  as  usual,  dark  blue  or  black. 

(2)  Human  cords  from  cases  which  have  lived  some  time  after  the  destruction 
of  the  motor  cortex,  or  after  interruption  of  the  motor  tract  in  any  part  of  its  course, 
may  also  be  used  for  studying  the  descending  fibre  tracts. 

(3)  The  cord  of  an  animal  may  be  cut  or  crushed,  the  animal  kept  alive  for 
from  two  weeks  to  several  months,  and  the  cord  then  treated  as  in  technic  1. 
The  most  satisfactory  animal  material  may  be  obtained  from  a  large  dog  by  cutting 
the  cord  half-way  across,  the  danger  of  too  early  death  from  shock  or  complica- 
tions being  much  less  than  after  complete  section. 

(4)  The  cord  of  a  human  foetus  from  the  sixth  month  to  term  furnishes  good 
material  for  the  study  of  the  anterior  and  posterior  root  fibres,  the  plexus  of  fine 
fibres  in  the  gray  matter,  the  groupings  of  the  anterior  horn  cells,  etc.  The  pyram- 
idal tracts  are  at  this  age  non-medullated  and  are  consequently  unstained  in  Wei- 
gert preparations.     The  Weigert-Pal  method  gives  the  best  results  (page  26). 

(5)  For  the  study  of  the  course  of  the  posterior  root  fibres  within  the  cord, 
cut  any  desired  number  of  posterior  roots  between  the  ganglia  and  the  cord  and 
treat  material  by  the  Marchi  or  the  Weigert  method,  according  to  the  time  elapsed 
between  the  operation  and  the  death  of  the  animal. 


THE    MEDULLA    OBLONGATA. 
(Including  the  Pons  Varolii.) 

The  medulla  oblongata  is  the  continuation  upward  of  the  spinai 
cord  and  extends  from  the  lower  limit  of  the  pyramidal  decussation 
below  to  the  lower  margin  of  the  midbrain  above. 

Externally,  the  medulla  shows  the  continuation  upward  of  the 
anterior  fissure  and  posterior  septum  of  the  cord.  On  either  side  of 
the  anterior  fissure  is  a  prominence  caused  by  the  anterior  pyramid, 
and  to  the  outer  side  of  the  pyramid  the  bulging  of  the  olivary  body 
may  be  seen.  The  anterolateral  surface  of  the  medulla  is  also 
marked  by  the  exit  of  the  fifth  to  the  twelfth  (inclusive)  cranial 
nerves.  The  posterior  surface  shows  two  prominences  on  either  side. 
The  more  median  of  these,  known  as  the  clava,  is  caused  by  the 
nucleus  gracilis,  or  nucleus  of  the  column  of  Goll ;  the  other,  lying 
just  to  the  outer  side  of  the  clava,  is  due  to  the  nucleus  cuneatus  cr 
nucleus  of  the  column  of  Burdach.  The  central  canal  of  the  cord 
continues  into  the  medulla,  where  it  gradually  approaches  the  dorsal 
surface,  and  about  the  middle  of  the  medulla  opens  into  the  cavity 
of  the  fourth  ventricle. 


o 


68  THE   ORGANS. 


The  internal  structure  of  the  medulla  considerably  resembles  that 
of  the  cord.  This  is  especially  true  of  the  lower  part  of  the  medulla, 
the  structures  of  which  are  directly  continuous  with  those  of  the  cord. 
The  fibre  tracts  of  the  cord,  however,  assume  in  the  medulla  new 
directions,  and  in  so  doing  break  up  the  formation  of  the  gray  mat- 
ter. This  and  the  appearance  of  certain  new  masses  of  gray  matter 
and  of  some  new  fibre  bundles,  many  of  them  connected  with  the 
cranial  nerves,  are  the  main  factors  determining  the  difference  in 
structure  between  cord  and  medulla. 

Of  the  ascending  tracts,  the  posterior  columns  end  in  the  nuclei 
of  Goll  and  Burdach,  whence  a  second  neurone  system  connects  them 
with  higher  centres,  the  axones  passing  up  mainly  in  the  fillet  and 
restiform  body;  the  direct  cerebellar  tract  passes  into  the  res tiform 
body,  while  the  tract  of  Gowers  continues  as  such  through  the 
medulla. 

Of  the  descending  tracts,  the  most  important,  the  direct  and 
crossed  pyramidal  tracts,  are  represented  in  the  medulla  by  the  ante- 
rior pyramids. 

Of  the  spinal  gray  matter,  there  are  still  remnants  which  form 
the  nuclei  of  termination  for  sensory  cranial  nerves,  the  largest  mass 
being  the  extended  nucleus  of  the  spinal  fifth.  The  anterior  horns 
'of  the  cord  are  represented  in  the  medulla  by  separate  masses  of  gray 
matter,  which  are  the  nuclei  of  origin  for  motor  cranial  nerves.  Of 
new  masses  of  gray  matter,  the  most  important  are  the  nuclei  of  the 
columns  of  Goll  and  of  Burdach  and  the  olivary  nucleus,  which  is 
connected  with  the  cerebellum  via  its  inferior  peduncle. 

The  cranial  nerves,  with  the  exception  of  the  first  (olfactory)  and 
the  second  (optic),  are  analogous,  both  embryologically  and  anatomi- 
cally, to  the  spinal  nerves. 

The  neurones  which  constitute  the  sensory  portions  of  the  cranial 
nerves  have  their  cell  bodies  situated  in  ganglia  outside  the  central 
nervous  system.  These  ganglia  correspond  to  the  posterior  root 
ganglia  of  the  spinal  nerves.  The  outwardly  directed  processes  of 
these  cells  pass  to  their  peripheral  terminations  as  do  those  of  the 
spinal  ganglion  cells.  The  central  axones  of  these  neurones  enter 
the  medulla  and  form  longitudinal  tracts  of  fibres  in  a  manner  quite 
analogous  to  the  formation  of  the  posterior  columns  by  the  ascending 
branches  of  the  central  axones  of  the  spinal  ganglion  cells.  The  longer 
branches  of  the  sensory  root  fibres  of  the  cranial  nerves,  however,  do 


THE  NERVOUS  SYSTEM.  369 

not  ascend,  as  do  those  of  the  spinal  nerves,  but  turn  spinalward, 
forming  descending  roots.  These  fibres  terminate  in  the  gray  mat- 
ter of  the  medulla  (terminal  nuclei  of  the  cranial  nerves)  in  the  same 
manner  as  do  the  spinal  sensory  root  fibres  in  the  gray  matter  of  the 
cord  and  medulla.  Thus  the  sensory  root  fibres  of  the  fifth  nerve 
form  a  distinct  bundle  known  as  the  spinal  root  of  the  fifth ;  some  of 
the  fibres  of  the  vestibular  part  of  the  eighth  nerve  form  another  dis- 
tinct bundle,  the  descending  root  of  the  eighth  ;  while  the  descending 
root  fibres  of  the  ninth  and  tenth  form  the  solitary  fasciculus. 
The  fibres  of  each  of  these  descending  roots  terminate  in  an  accom- 
panying nucleus.  The  axones  of  the  cells  of  these  terminal  nuclei 
form  secondary  ascending  tracts  to  higher  centres,  these  tracts  thus 
bearing  the  same  relation  to  the  cranial  nerves  that  the  fillet  does  to 
the  spinal. 

The  motor  root  fibres  of  the  cranial  nerves  are  the  axones  of 
neurones  whose  cell  bodies  are  situated  in  the  gray  matter  of  the 
medulla  and  parts  above  (motor  nuclei  of  the  cranial  nerves),  just  as 
the  motor  root  fibres  of  the  spinal  nerves  are  the  axones  of  neurones 
whose  cell  bodies  are  situated  in  the  gray  matter  of  the  cord  (anterior 
horns).  These  motor  nuclei  are  distributed  in  two  series,  one  situ- 
ated near  the  median  line,  the  other  more  laterally.  In  the  former 
series  are  the  motor  nuclei  of  the  third,  fourth,  sixth,  and  twelfth ;  in 
the  latter  are  the  motor  nuclei  of  the  fifth,  seventh,  ninth,  and  tenth. 
While  these  nuclei  are  the  nuclei  of  origin  of  the  motor  divisions  of 
the  cranial  nerves,  they  are  also  the  nuclei  of  termination  for  neu- 
rones of  higher  systems  which  serve  to  bring  these  peripheral  motor 
neurones  under  the  control  of  higher  centres. 

The  internal  structure  of  the  medulla  can  be  best  studied  by 
means  of  a  series  of  transverse  sections. 

TECHNIC. 

The  technic  of  the  medulla  is  the  same  as  that  of  the  cord  (page  340).  Trans- 
verse sections  should  be  cut  through  the  following  typical  levels,  stained  by  Wei- 
gert's  method  (page  25),  and  mounted  in  balsam  : 

1.  Through  the  pyramidal  decussation. 

2.  Through  the  sensory  decussation. 

3.  Through  the  lower  part  of  the  olivary  nucleus. 

4.  Through  the  middle  of  the  olivary  nucleus. 

q.  Through  the  exit  of  the  eighth  cranial  nerve. 

6.  Through  the  exits  of  the  sixth  and  seventh  cranial  nerves, 

24 


6/' 


THE   ORGANS. 


i.  Transverse  Section  of  the  Medulla  through  the  Decussation 
of  the  Main  Motor  Tracts  (Pyramidal  Decussation)  (Fig. 
241). 

Compare  the  section  with  the  section  of  the  cervical  cord  (page 
345  1  and  note  the  following  structures  studied  in  the  cord  sections  : 

1.  The  posterior  column:  (a)  The  column  of  Goll  (funiculus 
gracilis),  and  (/;)  the  column  of  Burdach  (funiculus  cuneatus)  remain 
as  in  the  cervical  cord. 

2.  The  lateral  column  :  (a)  The  crossed  pyramidal  tract  is  smaller 
owing  to  the  fact  that  fewer  fibres  have  crossed  to  it  from  the  ante- 

4     ,0  1  rior  pyramid  (see  8,  p.  371);    (b) 

the  tract  of  Gowers,  (c)  the  direct 
cerebellar  tract,  and  ((/)  von 
Monakow's  bundle  occupy  about 
the  same  positions  as  in  the 
cervical  cord  (Fig.  238). 

(While  the  general  locations 
of  these  lateral  column  tracts 
should  be  noted,  they  cannot  be 
differentiated  in  the  normal  adult 
human  medulla.) 

3.  The  anterior  column;  in- 
creased in  size.  This  is  due  to 
the  fact  that  fewer  fibres  have 
left  it  to  decussate  and  enter  the 
crossed  pyramidal  tracts  (see  8, 
p.  371).  Lateral  to  the  pyra- 
midal tract  are:  (a)  The  tract  of  Melweg,  (/;)  the  sulco-marginal 
tract,  and  (r)  the  anterior  ground  bundles,  occupying  about  the  same 
positions  as  in  the  cervical  cord. 

(These  subdivisions  of  the  anterior  column  cannot  usually  be  dis- 
tinguished in  the  normal  adult  human  medulla.) 

4.  The  posterior  horn.  This  is  larger,  especially  the  gelatinous 
substance  of  Rolando,  and  is  almost  entirely  separated  from  the 
rest  of  the  gray  matter,  being  connected  with  it  by  a  very  long,  slen- 
der cervix  or  neck  (Fig.   241). 

5.  The  anterior  horn  is  cut  off  from  the  rest  of  the  gray  matter 
by  decussating  pyramidal  fibres. 


FIG.  241.— Transverse  Section  of  the  Medulla 
at  the  Level  of  the  Pyramidal  Decussation. 
(Dejerine.)  /,  Posterior  column;  /a,  col- 
umn of  Goll;  id,  column  of  Burdach;  2, 
lateral  column  ;  j,  anterior  column  ;  4,  pos- 
terior horn  ;  5,  anterior  horn  ;  7,  reticular 
formation  ;  S,  decussation  of  the  pyramids  ; 
g,  dorsal  root  of  first  cervical  nerve;  /o, 
gelatinous  substance  of  Rolando  ;  x,  neck 
of  posterior  horn. 


THE  NERVOUS  SYSTEM.  371 

6.  The  central  canal  and  the  central  gelatinous  substance  are  the 
same  as  in  the  cervical  cord. 

Note  also  the  following  new  structures  : 

7.  The  reticular  formation  ;  beginning  to  show  in  this  section,  al- 
though not  so  well  developed  as  higher  up  in  the  medulla.  Its  coarse 
basketwork  appearance  is  due  to  a  breaking-up  of  the  lateral  gray 
matter  by  longitudinal  fibres- — mainly  continuations  into  the  medulla 
of  the  lateral  fundamental  column  fibres  of  the  cord. 

8.  Decussation  of  the  pyramids.  This  is  the  most  important  fea- 
ture of  the  section.  Bundles  of  fibres  are  seen  crossing  from  the 
anterior  pyramid  of  one  side  to  the  opposite  dorso-lateral  column, 
where  they  turn  downward  as  the  crossed  pyramidal  tract.  These 
fibres,  as  already  noted  in  the  cord,  are  descending  axones  from  motor 
cells  situated  in  the  cerebral  cortex.  In  the  pyramidal  decussation 
most  of  these  fibres  cross  to  the  opposite  postero-lateral  region  to 
pass  down  the  cord  as  the  crossed  pyramidal  tract  (p.  362,  and  Fig. 
236,5;  Fig-  238,  /).  A  few  remain  in  their  original  anterior  po- 
sition to  continue  down  the  cord  as  the  direct  pyramidal  tract  (p. 
362,  and  Fig.  236,  /;  Fig.  238,  2).  The  bundles  of  fibres  do  not 
cross  in  a  transverse  plane,  but  take  a  downward  direction  at  the 
same  time.  For  this  reason  transverse  sections  show  these  fibres 
cut  rather  obliquely.  Because  of  the  fact  that  the  fibres  cross  in 
alternate  bundles,  the  number  of  decussating  fibres  seen  in  any  one 
section  is  greater  on  one  side  than  on  the  other  (Fig.  241). 

9.  The  dorsal  root  of  the  first  cervical  nerve. 

2.  Transverse  Section  of  the  Medulla  through  the  Decussation 
of  the  Fillet  (Sensory  Decussation)  (Fig.  242). 

Note  the  following  already  mentioned  structures  : 

1.  The  posterior  column.  Both  the  column  of  Goll  (<?)  and  the 
column  of  Burdach  (/?)  are  diminished  in  size,  being  shortened  dorso- 
ventrally  by  two  new  masses  of  gray  matter,  one  in  the  ventral  part 
of  each  column  (see  1  1,  p.  ^/^). 

2.  The  lateral  column  ;  much  depleted  in  size.  This  is  due  to 
the  absence  of  the  crossed  pyramidal  fibres,  as  this  section  is  above 
the  upper  limit  of  the  pyramidal  decussation,  and  the  descending  mo- 


o/- 


THE  ORGANS. 


tor  fibres  are  now  contained  in  the  anterior  pyramids  (see  8,  p.  371). 
Gowers'  tract,  the  direct  cerebellar  tract,  von  Monakow's  bundle,  and 
those  fibres  of  the  lateral  ground  bundles  which  have  not  entered  the 
reticular  formation  are  in  about  the  same  positions  as  in  the  previous 
section. 

3.  The  anterior  column;  increased  in  size,  now  containing  all  of 
the  descending   cerebro-smnal  fibres.     The  tract  of  Helweg   is   in 

about  the  same  position  as  in 
the  previous  section.  The 
sulco-marginal  tract  and  part 
of  the  anterior  ground  bundles 
lie  more  dorsal  just  lateral  to 
the  fillet,  where  they  form  the 
posterior  longitudinal  fascic- 
ulus (see  2i,  p.  375). 

4.  The  posterior  horn; 
larger  than  in  the  preceding 
section,  is  now  the  terminal 
nucleus  of  the  descending 
(sensory)  root  fibres  of  the 
fifth  nerve  (see  page  374). 

5.  The  anterior  horn.  This 
is  now  less  definite,  owing  to 
its  being  broken  up  by  bun- 
dles of  longitudinal  fibres,  and 
forms  a  part  of  the  reticular 
formation. 

6.  The  central  canal  and 
the  central  gelatinous  sub- 
stance ;   remain  the  same. 

7.  The  reticular  formation  ;    now  considerably  more  extensive. 

8.  The  decussation  of  the  pyramids.  This  has  almost  ceased,  al- 
though a  few  fibres  may  still  be  seen  passing  from  the  anterior  pyra- 
mid to  the  opposite  dorso-latcral  region,  and  a  wedge-shaped  mass 
of  its  fibres,  decussating  in  the  median  line,  may  often  be  noticed  in 
the  lower  levels  of  the  sensory  decussation. 

9.  The  dorsal  root  of  the  first  cervical  nerve  has  disappeared, 
while  the  gelatinous  substance  of  Rolando  has  become  a  part  of  4, 
the  remains  of  the  posterior  horn. 


FIG.  242.  —  Transverse  Section  of  the  Medulla 
through  the  Lower  Part  of  the  Sensory  De- 
cussation. (Dejerine.)  /,  Posterior  column  ; 
i  a,  column  of  Goll ;  //),  column  of  Burdach  ; 
2,  lateral  column  ;  j,  anterior  column  or  pyra- 
mid ;  4,  posterior  horn  ;  j,  anterior  horn  ;  7, 
reticular  formation  ;  A'G,  nucleus  gracilis  or 
nucleus  of  the  column  of  Goll;  NB,  nucleus 
cuneatus  or  nucleus  of  the  column  of  Burdach  ; 
12,  internal  arcuate  fibres;  ij,  sensory  decus- 
sation or  decussation  of  fillet  ;  ij,  spinal  root 
of  fifth  nerve;  /Vxi,  nucleus  of  origin  of  elev- 
enth cranial  nerve  ;  XI,  root  fibres  of  eleventh 
cranial  nerve. 


THE  NERVOUS  SYSTEM. 


373 


Nxi 


The  following  new  structures  are  to  be  observed : 
1 1.  The  nuclei  of  the  posterior  columns.  These  occupy  the  ven- 
tral part  of  the  columns  and  are  known  respectively  as  the  nucleus  of 
the  column  of  Goll,  or  the  nucleus  gracilis  (Fig.  242,  NG)  and  the 
nucleus  of  the  column  of  Burdach,  or  the  nucleus  cuneatus  (Fig.  242, 
NB).  In  the  higher  sensory  levels, there  is  usually  an  accessory 
cuneate  nucleus  (Fig.  243, 
NBa). 

These  nuclei  serve  as 
nuclei  of  termination  for 
the  fibres  of  the  posterior 
columns.  With  their  ter- 
mination in  these  nuclei  wc 
come  to  the  ending  of  that 
system  of  fibres  which  we 
have  traced  from  their 
origin  in  the  cells  of  the 
spinal  ganglia.  In  other 
words,  we  have  completed 
the  course  of  the  spinal 
peripheral  sensory  neu- 
rone. As  the  fibres  of  the 
posterior  columns  are  con- 
stantly terminating  in 
these  nuclei,  there  is,  in 
passing  from  below  up- 
ward, a  constant  increase 
in  the  size  of  the  nuclei 
and  a  corresponding  de- 
crease in  the  size  of  the 
posterior  columns,  until 
just  below  the  olive,  the 
whole  of  the  column  of 
Goll  and  most  of  the  col- 
umn of  Burdach  are  occupied  by  their  respective  nuclei  (Fig.  243, 
NG  and  NB).  By  means  of  neurones  whose  cell  bodies  are  situ- 
ated in  these  nuclei,  the  sensory  conduction  path  is  continued  brain- 
ward.  These  neurones  may  be  separated  into  four  systems :  (a) 
An  uncrossed  tract  through  the  restiform  body  of  the  same  side  to 


XII 


FIG.  243. —Transverse  Section  of  the  Medulla  through 
the  Upper  Part  of  the  Sensory  Decussation.  (De- 
jerine.)  /,  Posterior  column  ;  /  a,  column  of  Goll  ; 
lb,  column  of  Burdach  ;  NG,  nucleus  gracilis  or  nu- 
cleus of  the  column  of  Goll  ;  A'B,  nucleus  cuneatus 
or  nucleus  of  the  column  of  Burdach;  A'B:i,  ex- 
ternal or  accessory  cuneate  nucleus  ;  Fit.  lateral 
column;  3,  anterior  column  or  pyramid;  SgR, 
gelatinous  substance  of  Rolando  and  remains  of 
posterior  horn  ;  j,  anterior  horn  ;  SRg,  reticular 
formation  ;  12,  internal  arcuate  fibres  ;  13,  sensory 
decussation  ;  14,  fillet ;  ij,  spinal  root  of  fifth  nerve  ; 
XI,  root  fibres  of  eleventh  cranial  nerve  ;  Nxi, 
nucleus  of  eleventh  cranial  nerve  ;  ij,  accessory 
olivary  nucleus;  cOi,  olivary  fibres;  1$,  arciform 
nucleus;  iq,  solitary  fasciculus;  Nxii,  nucleus  of 
twelfth  cranial  nerve,  XII,  root  fibre  of  twelfth 
cranial  nerve  ;  22,  external  arcuate  fibres;  23,  resti- 
form body;  24,  olivary  nucleus. 


374  THE   ORGANS. 

the  cerebellum.  {b)  A  crossed  tract  through  the  opposite  restiform 
body  to  the  cerebellum  (see  page  375,  22).  (c)  A  crossed  tract  to 
the  optic  thalamus.  (d)  A  crossed  tract  to  the  cerebral  cortex. 
The  fibres  of  (c)  and  (d )  as  : 

12.  Internal  arcuate  fibres,  pass  ventrally  and  inward  from  the 
nuclei  of  the  posterior  columns  to  a  point  just  below  the  central 
canal,  where  they  form  the 

13.  Sensory  decussation,  or  decussation  of  the  fillet.  These  fibres 
are  axones  of  neurones  whose  cell  bodies  are  situated  in  the  nuclei  of 
the  posterior  columns.  After  decussating  they  turn  brainward,  form- 
ing a  tract  of  fibres  known  as  the 

14.  Fillet,  or  median  lemniscus,  which  lies  just  dorsal  to  the 
anterior  pyramid,  and  increases  in  size  as  we  ascend  through  this 
level. 

15.  Spinal  (descending)  root  of  the  fifth  cranial  nerve  (trigemi- 
nus). This  is  a  bundle  of  very  fine  fibres  lying  vjust  external  to  the 
posterior  horn,  thus  occupying  the  position  of  Lissauer's  column  in 
the  cord.  From  this  bundle,  fibres  can  be  seen  entering  the  remains 
of  the  posterior  horn,  which,  as  stated  above  (page  368),  is  its  termi- 
nal nucleus.  The  neurones  of  the  latter  constitute  the  secondary 
sensory  (ascending)  tract  for  the  fifth  nerve,  as  do  those  of  the  nuclei 
of  Goll  and  Burdach  for  spinal  sensory  nerves. 

16.  The  nucleus  of  origin  of  the  eleventh  cranial  (spinal  accessory) 
nerve  (Nxi)  and  its  root  fibres  {XI)  passing  toward  the  surface. 

The  following  new  structures  are  to  be  seen  only  in  the  higher 
levels  of  the  sensory  decussation  (Fig.  243). 

17.  The  accessory  olivary  nucleus;  an  elongated  L-shapcd 
mass  of  gray  matter  lying  just  dorsal  to  the  anterior  pyramid. 

[8,  The  arciform  nucleus;  on  the  surface  of  the  medulla  ven- 
tral to  the  anterior  pyramid. 

19.  The  solitary  fasciculus.  This  shows  in  some  of  the  sections 
as  a  distinct  round  bundle  of  fibres  just  lateral  to  the  central  gray 
matter.  It  consists  of  the  descending  or  sensory  root  fibres  of  the 
ninth  (glossopharyngeal)  and  tenth  (vagus)  cranial  nerves.  The 
gray  matter  in  its  immediate  vicinity  is  its  terminal  nucleus. 

20.  (Nxii)  The  nucleus  of  origin  of  the  twelfth  cranial  nerve 
(hypoglossal).  This  is  a  group  of  nerve  cells  lying  in  the  ventral 
part  of  the  central  gelatinous  substance,  near  the  median  line.     Root 


THE  NERVOUS  SYSTEM. 


375 


d.n.X  X/ 


fibres  of  this  nerve  may  be  seen  passing  from  the  nucleus  to  the  ven- 
tral surface  of  the  cord  {XII). 

21.  The  posterior  longitudinal  fasciculus;  a  bundle  of  fibres 
situated  just  dorsal  to  the  fillet.  These  fibres  are  the  upward  con- 
tinuation    of      the     anterior 

ground  bundles  of  the  cord 
and  of  the  sulcomarginal 
tract. 

22.  The  external  arcuate 
fibres.  These  are  often  pres- 
ent at  this  level  running 
parallel  to  the  lateral  surface 
of  the  cord  just  under  the  pia 
mater.  They  are,  at  this 
level,  axones  of  neurones 
whose  cell  bodies  are  situ- 
ated in  the  nucleus  gracilis 
and  nucleus  cuneatus 
axones  pass  first  as  internal, 
then  as  external,  arcuate  fibres 
to  the  restiform  body,  thence 
to  the  cerebellum  (p.  374,  1 1 
b,  and  Fig.  264,  E,  2d).  It 
is  probable  that  some  of  these 
fibres  end  among  cells  of  the 
arciform  nucleus.  Dorsal  ex- 
ternal arcuate  fibres  may  also 
often    be    seen.      These    are 

fibres  from  the  columns  of  Goll  and  Burdach,  or  axones  from  cells 
of  their  nuclei  passing  to  the  restiform  body  of  the  same  side  (p. 
373,  11  a,  and  Fig.  264,  E,  2c). 

23.  The  restiform  body.  This  appears  in  the  higher  sensory  de- 
cussation levels  as  a  narrow  band  of  fibres  along  the  lateral  margin 
of  the  medulla.      (For  details  see  page  380,  23.) 

24.  The  olivary  nucleus.  This  may  sometimes  be  seen  as  one  or 
two  small  masses  of  gray  matter  dorso- lateral  to  the  accessory  olive. 
(For  details  see  page  ^77>  24-) 


These  ^IG-  244-  — Diagram  of  Origin  of  Cranial  Nerves  X 
and  XII.  (Schafer.)  pyr.  Pyramid;  o,  olivary 
nucleus;  ;-,  restiform  body;  d.  V,  spinal  root  of 
fifth  nerve  ;  n.XII,  nucleus  of  hypoglossal  ;  XII, 
hypoglossal  nerve  ;  d.n.X.  XI,  dorsal  nucleus  of 
vagus  and  spinal  accessor}-  ;  n.amb,  nucleus  am- 
biguus;  f.s,  solitary  fasciculus  (descending  root 
of  vagus  and  glosso-pharyngeal);  f.s.n,  nucleus  of 
solitary  fasciculus  ;  X,  motor  fibre  of  vagus  from 
nucleus  ambiguus  ;  g,  ganglion  cell  of  sensory 
root  of  vagus  sending  central  arm  into  solitary 
fasciculus  (f.s)  and  collateral  to  its  nucleus 
( f.s.n.);  f.s. ?i,  cell  of  nucleus  of  solitary  fasciculus 
sending  axone  as  internal  arcuate  fibre  to  opposite 
side  of  cord  (secondary  vagus  and  glosso-pharyn- 
geal  tract). 


376 


THE  ORGANS. 


3.  Transverse  Section  of  the  Medulla  through  the  Lower   Part 
of  the  Olivary  Nucleus  (Fig.  245). 

Note  the  following  already  mentioned  structures : 

1.  The  posterior  column,  which  has  almost  disappeared,  its  fibres 
having  passed  into  the  posterior  column  nuclei. 

2.  The   lateral   column.      This   still   contains   Gowers'   tract,  the 
direct  cerebellar  tract,  and  von  Monakow's  bundle. 

jrxn: 


FlG.  245.-Transver.se  Section  of  the  Medulla  through  the  Lower  Part  of  the  Olivary  Nucleus. 
(Dejerine.)  /,  Posterior  column  ;  2,  lateral  column;  3,  pyramid  ;  SgR,  gelatinous  sub- 
stance of  Rolando  and  remains  of  posterior  horn  ;  j,  remains  of  anterior  horn  ;  A'C'/,  nu- 
cleus of  the  posterior  [column  ;  /?,  internal  arcuate  fibres;  /j,  sensory  decussation;  74, 
fillet ;  /j,  spinal  root  of  fifth  cranial  nerve  ;  77,  accessory  olivary  nuclei  ;  /y  a,  dorsal  acces- 
sory olivary  nucleus;  /,?,  arcuate  nucleus;  jq,  solitary  fasciculus;  JVxfi,  nucleus  of 
twelfth  cranial  nerve;  A'//,  root  fibres  of  twelfth  cranial  nerve;  posterior  longitudinal 
fasciculus  just  ventral  to  Xxii  but  not  distinguishable  from  the  fillet;  22,  external  arcu- 
ate fibres;  x,  cerebello-olivary  fibres  ;  23,  restiform  body  ;  .?,/,  olivary  nucleus  ;  sj,  fourth 
ventricle;  26,  dorsal  nucleus  of  ninth  ami  tenth  nerves;  27,  nucleus  ambiguus;  fio,  oli- 
vary fibres. 

3.  The  anterior  column  (anterior  pyramid) ;  now  consists  almost 
wholly  of  pyramidal  tract  fibres. 

4.  The  posterior  horn  ;  somewhat  diminished  in  size. 

5.  The  anterior  horn.  This  is  now  largely  lost  in  the  reticular 
formation,  part  of  the  gray  matter  of  which  is  its  upward  continu- 
ation. 

6.  The   centra]   canal;    now   opening   into   the   fourth   ventricle, 


THE  NERVOUS  SYSTEM.  377 

the  gelatinous  substance  and  the  nuclei  of  the  floor  of  the  ventricle 
constituting  the  central  gray  matter. 

7.  The  reticular  formation  ;  occupying  a  much  larger  area  than 
in  the  preceding  section  (between  SgR  and  median  line). 

11.  The  nuclei  of  the  posterior  column  {NCp)  ;  diminished  in 
size  and  not  clearly  defined. 

12.  The  internal  arcuate  fibres  ;   more  numerous. 

13.  The  sensory  decussation  or  decussation  of  the  fillet;  now 
more  extended  dorso-ventrally,  forming  the  median  raphe. 

14.  The  fillet  or  median  lemniscus;  larger,  more  of  the  decus- 
sating fibres  having  now  joined  it. 

15.  The  spinal  root  of  the  fifth  cranial  nerve  (trigeminus); 
larger,  as  fewer  fibres  have  left  it  to  terminate  in  the  gray  matter. 

17.  The  accessory  olivary  nucleus  ;  smaller  than  in  the  preceding 
section. 

18.  The  arciform  nucleus. 

19.  The  solitary  fasciculus  (see  p.  374,  19). 

20.  The  nucleus  of  origin  (Alrii)  of  the  twelfth  cranial  nerve 
(hypoglossal)  (see  p.  374,  20)  and  the  root  fibres  of  the  nerve  (XII) ; 
passing  along  the  lateral  margin  of  the  fillet  and  thence  to  the  sur- 
face between  the  olivary  nucleus  and  the  anterior  pyramid  (Fig.  245). 

21.  The  posterior  longitudinal  fasciculus;  now  more  dorsal  and 
not  easily  differentiated  at  this  level  from  the  fillet. 

22.  The  external  arcuate  fibres;  more  numerous  than  in  the  pre- 
ceding section.  Some  of  the  more  dorsal  of  these  fibres  are  fibres  of 
the  direct  cerebellar  tract  passing  to  the  restiform  body. 

23.  The  restiform  body;  larger  and  not  extending  as  far  ven- 
trally.      (For  details  see  p.  380,  23.) 

24.  The  olivary  nucleus.  This  is  now  an  irregularly  convoluted 
lamina  of  gray  matter,  dorso-lateral  to  the  anterior  pyramid.  Note 
the  fibres  which  pass  as  internal  arcuate  fibres  from  each  olive 
through  the  median  raphe  to  the  opposite  restiform  body  (Fig.  245, 
.1)  and  thence  to  the  cerebellum  (cerebello-olivary  fibres).  Some 
of  these  latter  are  probably  ascending  axones  from  cells  in  the 
olivary  nucleus ;  others  are  probably  descending  axones  from  cells 
in  the  cerebellum.  Fibre  tracts  also  connect  the  olives  with  the 
cord,  passing  through  the  ventral  and  lateral  ground  bundles.  It  is 
uncertain  whether  these  are  descending  or  ascending  fibres,  or  both 
(see  Fig.  264,  Neurone  No.  8). 


378  THE   ORGANS. 

Note  the  following  new  structures  : 

i  j  a.   Dorsal  accessory  olivary  nucleus. 

25.  The  fourth  ventricle,  or  cavity  of  the  medulla  into  which  the 
central  canal  has  now  opened. 

26.  The  dorsal  nucleus  of  the  ninth  1  glossopharyngeal)  and  tenth 
(vagus)  cranial  nerves;  a  group  of  cells  lying  just  to  the  outer  side 
of  the  nucleus  of  the  twelfth  nerve.  The  dorsal  part  of  the  nucleus 
belongs  to  the  ninth,  the  ventral  to  the  tenth  nerve  (Fig.  245). 

27.  The  nucleus  ambiguus,  motor  nucleus  of  the  ninth  and  tenth 
cranial  nerves;  often  difficult  to  distinguish,  lies  in  the  lateral  part 
of  the  reticular  formation.  From  the  cells  of  this  nucleus  fibres  pass 
dorsally  to  just  below  the  sensory  nuclei  of  their  nerves,  where  they 
turn  sharply  ventro-laterally  and  join  the  sensory  root  fibres  (Fig. 
244). 

28.  The  root  fibres  of  the  tenth  cranial  nerve  (vagus)  (Fig. 
245,  X). 

4.  Transverse  Section  of  the  Medulla  through  the  Middle  of  the 
Olivary  Nucleus  (Ninth  and  Tenth  Nerves)  (Fig.  246). 

The  following  structures  present  in  the  last  section  have  now 
disappeared  : 

1.   The  posterior  column. 

5.  The  anterior  horn. 

6.  The  central  canal. 

1  1.   The  nuclei  of  the  posterior  column. 
13.   The  sensory  decussation. 

Note  the  following  structures  seen  in  last  section  : 

2.  The  lateral  column.  The  direct  cerebellar  tract  is  now  a  part 
of  the  restiform  body.  (lowers'  tract  and  von  Monakow's  bundle  oc- 
cupy about  the  same  positions  as  in  the  preceding  section. 

3.  The  anterior  pyramid  ;  remains  the  same. 

4.  The  posterior  horn  ;   smaller  and  more  vague. 

7.  The  reticular  formation  (SRg)\  increased  in  extent,  reaching 
its  maximum  in  this  and  the  next  succeeding  level. 

12.  The  internal  arcuate  fibres  ;  no  longer  derived  mainly  from 
the  posterior  column  nuclei;  being  now  largely  decussating  fibres 
from  sensory  cranial  nerve  nuclei  and  from  other  nuclei  in  the  reticu- 


THE  NERVOUS   SYSTEM. 


379 


lar  formation.  Many  internal  arcuate  fibres  also  represent  cerebello- 
olivary  fibres  connecting  the  restiform  body  with  the  opposite 
olive. 

14.  The  fillet,  or  median  lemniscus  (SRa);  now  completely 
formed  and  much  extended  dorso-ventrally.  While  the  fillet  must 
be  regarded  as  the  main  continuation  brainward  of  the  spinal  sen- 
sory conduction  path,  other  fibres  enter  into  its  formation.  Thus 
we  find  in  the  fillet  axones  of  cells  situated  in  the  reticular  formation 


ITrair- 


FlG.  246.— Transverse  Section  of  the  Medulla  through  the  Middle  of  the  Olivary  Nucleus. 
(Dejerine.)  2,  Lateral  column  ;  3,  pyramid;  4,  gelatinous  substance  of  Rolando  and  re- 
mains of  posterior  horn;  Sftg,  reticular  formation;  J2,  internal  arcuate  fibres  ;  S/?j, 
fillet;  jj,  spinal  root  of  fifth  cranial  nerve;  jy,  accessory  olivary  nucleus;  iS,  arciform 
nucleus;  jq,  solitary  fasciculus;  Nxii,  nucleus  of  origin  of  twelfth  cranial  nerve;  from 
the  nucleus  fibres  can  be  seen  passing  ventrally  just  to  the  mesial  side  of  the  olivary  nu- 
cleus ;  posterior  longitudinal  fasciculus  just  ventral  to  jo  but  not  distinguishable  from 
the  fillet  ;  22,  external  arcuate  fibres  ;  2j,  restiform  body  :  25,  fourth  ventricle  ;  26,  dorsal 
nucleus  of  ninth  and  tenth  cranial  nerves  ;  2j,  nucleus  ambiguus  ;  A",  root  fibres  of  tenth 
nerve;  Nviiir,  spinal  root  of  vestibular  division  of  eighth  nerve  ;  jo,  nucleus  of  funiculus 
teres  ;  Cj,  gray  matter  adjacent  to  the  restiform  body,  sometimes  called  the  corpus j'uxta- 
restiforme ;  Nr,  nucleus  of  the  reticular  formation;  .r,  nucleus  of  the  restiform  body; 
c,  choroid  plexus. 

of  the  medulla  and  of  the  pons,  also  axones  from  the  nuclei  of  termi- 
nation of  the  sensory  cranial  nerves.  The  termination  of  the  fillet 
is  also  very  complex.  Though  the  majority  of  its  fibres  terminate  in 
the  nuclei  of  the  thalamus,  some  may  pass  directly  to  the  cerebral 
cortex,  while  still  others  end  in  the  gray  matter  of  the  medulla  (espe- 
cially of  the  olives),  pons,  midbrain,  and  hypothalamic  region. 


380  THE   ORGANS. 

15.  The  spinal  root  of  the  fifth  nerve;  larger,  for  the  same  reason 
as  in  the  last  section. 

17.  The  accessory  olive;  may  be  present  or  absent.  There  may 
be  a  dorsal  accessory  olive  just  above  the  inner  end  of  the  main 
olivary  nucleus. 

iS.    The  arciform  nucleus;   usually  present. 

19.  The  solitary  fasciculus;  now  larger  and  more  distinct.  In 
some  sections,  some  of  the  sensory  root  fibres  of  the  ninth  and  tenth 
nerves  can   hi  seen  passing  into  the  solitary  fasciculus  (see  also  p. 

374,  19)- 

20.  The  nucleus  of  origin  of  the  twelfth  cranial  nerve  (hypoglos- 
sal) {Xxii) ;  about  the  same  size  as  in  the  preceding  section.  From 
it  are  seen  passing  out  the  root-fibres  of  the  twelfth  nerve  {XII). 

21.  The  posterior  longitudinal  fasciculus;  dorsal  to  the  fillet  and 
not  distinguishable  from  the  latter  at  this  level. 

22.  External  arcuate  fibres.  These  may  be  seen  running  par- 
allel to  the  surface  of  the  medulla  just  under  the  pia  mater. 

23.  The  restiform  body;  much  larger  than  in  the  last  section. 
Note  along  its  lateral  margin  a  narrow  strip  of  gray  matter,  the  nu- 
cleus of  the  restiform  body  (Fig.  246,  .1). 

The  restiform  body  or  inferior  cerebellar  peduncle  now  contains 
fibres  from  the  nuclei  of  the  posterior  columns  of  both  the  same  and 
opposite  sides  (internal  and  external  arcuate  fibres)  and  from  the  col- 
umns of  Goll  and  Burdach  direct  (p.  375,  22,  p.  373,  1  1)  ;  fibres  con- 
necting the  olivary  nucleus  with  the  cerebellum  (p.  377,  24) ;  fibres 
which  represent  the  continuation  upward  of  the  direct  cerebellar 
tract  (see  diagram,  Fig.  264). 

24.  The  olivary  nucleus  ;  larger  than  in  the  preceding  section. 
(For  details  see  p.   377,  24.) 

25.  The  fourth  ventricle;  more  widely  open.  Note  its  roof  now 
formed  by  the  choroid  plexus. 

26.  The  dorsal  nucleus  of  the  ninth  and  tenth  nerves;  about  the 
same  size,  but  nearer  the  ventricle  (see  p.   378,  26). 

27.  The  nucleus  ambiguus ;  about  the  same  as  in  the  preceding 
section. 

2.S.    (.V  )   Root  fibres  of  the  ninth  and  tenth  cranial  nerves. 

Note  the  following  structures  not  present  in  the  preceding  section  : 
29.    The  descending  or  spinal  root  of  the  vestibular  portion  of  the 


THE  NERVOUS  SYSTEM.  381 

eighth  cranial   nerve  (auditory)  (Nviiir);   in  the  lateral  wall  of  the 
fourth  ventricle.      (For  details  see  p.  383,  Figs.  247  and  248.) 
30.   The  nucleus  of  the  funiculus  teres. 

5.  Transverse  Section  of  the  Medulla  through  the  Exit  of  the 
Eighth  Nerve  (Fig.  247). 

The  following  structures  present  in  the  preceding  section  have 
now  disappeared : 

17.  The  accessory  olives;  although  a  small  dorsal  or  internal  ac- 
cessory olive  may  be  present. 

19.  The  solitary  fasciculus. 

20.  The  nucleus  of  origin  of  the  twelfth  cranial  nerve. 

26.  The  dorsal  nucleus  of  the  ninth  and  tenth  nerves. 

27.  The  nucleus  ambiguus. 

28.  The  root  fibres  of  the  ninth  and  tenth  nerves. 

29.  The  spinal  root  of  the  vestibular  portion  of  the  eighth  nerve. 

30.  The  nucleus  of  the  funiculus  teres. 

Note  the  following  structures  seen  in  the  preceding  section  : 

2.  The  remains  of  the  lateral  column  (containing  Gowers'  tract 
and  von  Monakow's  bundle). 

3.  The  anterior  pyramid. 

4.  The  remains  of  the  posterior  horn. 
7.  The  reticular  formation  {SR). 

12.  The  internal  arcuate  fibres. 

14.  The  fillet. 

15.  The  spinal  root  of  the  fifth  nerve;  increased  in  size. 

18.  The  arciform  nucleus  (Narc). 

21.  The  posterior  longitudinal  fasciculus. 

22.  The  external  arcuate  fibres. 

23.  The  restiform  body;  much  larger,  being  now  almost  com- 
pletely formed.  If  the  roof  of  the  fourth  ventricle  and  part  of  the 
cerebellum  be  included  in  the  section,  the  restiform  body  can  be  seen 
passing  into  the  cerebellum  as  its  inferior  peduncle. 

24.  The  olivary  nucleus;   much  reduced  in  size. 

25.  The  fourth  ventricle  with  the  choroid  plexus  in  its  roof. 

The  following  new  structures  are  to  be  noted  : 

31.    {VIII)   The  root  fibres  of  the  eighth    cranial  nerve   (audi- 


382 


THE   ORGANS. 


tory)  and  its  nuclei  (see  also  Fig.  248).  The  auditory  nerve  is  divided 
into  two  parts  :  the  cochlear  nerve  and  the  vestibular  nerve.  The 
fibres  of  the  cochlear  root  (l^IIIc)  enter  at  a  lower  level  than  those 
of  the  vestibular.  Some  of  them  enter  a  nucleus  ventral  to  the 
restiform  body  (ventral  cochlear  nucleus)  (Nviii,  c) ;  the  remainder 
12  Tvfra.      34 


Time 


FIG.  247. — Transverse  Section  of  tiie  Medulla  through  the  Upper  Fart  of  the  Olivary  Nucleus 
and  Exit  of  the  Eighth  Cranial  Nerve.  CDejerine.)  2,  Remains  of  lateral  column;  3, 
pyramid  ;  4.  remains  of  posterior  horn  serving  as  terminal  nucleus  for  spinal  root  of  fifth 
nerve  ;  S/\.  reticular  formation  ;  13,  internal  arcuate  fibres  ;  /•,-,  spinal  root  of  fifth  nerve  ; 
.Wire,  annate  nucleus;  .?/,  posterior  longitudinal  fasciculus;  22,  external  arcuate  fibres, 
mainly  cerebello-olivary  fibres;  2j,  restiform  body  ;  24,  olivary  nucleus;  23,  fourth  ven- 
tricle ;  VJlIc,  cochlear  root  of  the  eighth  cranial  nerve  ;  VJIlv,  vestibular  root  of  eighth 
al  nerve;  Nviiic,  ventral  cochlear  nucleus;  XI),  Deiter's  nucleus;  Xviiiv,  median 
or  principal  vestibular  nucleus  ;  /'//.  root  fibres  of  seventh  cranial  nerve;  Nvii,  nucleus 
of  origin  of  seventh  cranial  nerve;  /'/,  root  fibres  of  sixth  cranial  nerve;  .,-y,  acoustic 
striae;  jy,  transverse  pontile  fibres  ;  37,  central  tegmental  tract  ;  Nci,  nucleus  of  the  retic- 
ular I":  mat  ion  ;  Xr.  nucleus  of  the  median  raphe  ;    Tr,  trapezoid  body. 

pass  dorsal  ward  to  a  nucleus  external  to  the  restiform  body  (dorsal - 
cochlear  nucleus,  or  nucleus  of  the  aroustic  tubercle)  (seen  only  in 
lower  sections  of  this  level). 


THE  NERVOUS  SYSTEM. 


333 


The  fibres  of  the  vestibular  root  (  VIII,  v)  enter  above  and  mesial 
to  those  of  the  cochlear  root,  passing  dorsally  along  the  inner  side  of 
the  restiform  body  to  four  nuclei,  which  cannot  all  be  clearly  seen 
in  any  one  section;  (a)  Deiter's  nucleus  (lateral  vestibular  nucleus) 
(ND),  situated  at  the  end  of  the  main  bundle  of  root  fibres,  just  in- 
ternal to  the  restiform  body;  (/>)  von  Bechterew's  nucleus  (superior 
vestibular  nucleus)  situated  somewhat  dorsal  to  Deiter's  nucleus 
in  the  lateral  wall  of  the  fourth  ventricle;  (c)  the  median  or  princi- 
pal nucleus  of  the  vestibular  division — a  large  triangular  nucleus, 
occupying    the    greater  part    of    the    floor    of    the    fourth   ventricle 


Fig.  248.— Diagram  of  Origin  of  Eighth  Cranial  Nerve  and  some  of  its  more  Important  Central 
Connections.  (Obersteiner.)  Cbfl,  Cerebellum  ;  Crst,  restiform  body;  Co,  cerebral  cor- 
tex; Py,  pyramid;  Ra,  median  raphe;  Va,  spinal  root  of  fifth  nerve;  NVI,  nucleus  of 
sixth  nerve;  VI,  root  fibres  of  sixth  nerve  ;  VJI  root  fibres  of  seventh  nerve  ;  Rl,  cochlear 
root  of  eighth  nerve  (axones  of  cells  in  spinal  ganglion  or  ganglion  of  Corti)  passing  to 
their  terminations  in  the  ventral  cochlear  nucleus,  Xacc,  and  iu  the  dorsal  cochlear  nu- 
cleus, Tba :  Rm,  vestibular  root  of  eighth  nerve  (axones  of  cells  in  Scarpa's  ganglion) 
passing  to  their  terminations  in  Deiter's  nucleus,  XD,  and  in  the  median  vestibular  nu- 
cleus, Ntr  (the  nucleus  of  von  Bechterew  and  the  spinal  vestibular  nucleus  are  not  seen 
at  this  level);  Strm,  stria?  acustica?  ;  Tgm.  tegmentum  ;  Os.  superior  olivary  nucleus;  Ost, 
fibres  from  superior  olivary  nucleus  to  nucleus  of  sixth  nerve;  Nt,  trapezoid  nucleus; 
dr.  trapezoid  body;  Ltnl,  lateral  lemniscus  or  lateral  fillet;  Qa,  anterior  corpus  quad- 
rigeminum  ;  Qp,  posterior  corpus  quadrigeminum. 


{Xviii,  v) ;  and  (J)  the  spinal  vestibular  nucleus  which  accompa- 
nies the  descending  fibres  of  the  vestibular  root  (spinal  eighth,  see 
p.   380,  29). 

The  fibres  of  the  cochlear   nerve  are  axones   of  bipolar  cells   in 
the  spiral  ganglion,  or  ganglion  of  Corti  (see  p.  439,  Fig.  283).      The 


384  THE   ORGANS. 

central  processes  of  these  cells  enter  the  medulla  as  the  above-de- 
scribed cochlear  root,  to  terminate  in  arborizations  among  the  cells 
of  the  cochlear  nuclei.  Most  of  the  axones  of  the  cells  of  these 
nuclei  cross  to  the  opposite  side  of  the  medulla,  forming  the  second- 
ary cochlear  tract  to  higher  centres,  known  as  the  lateral  fillet 
(see  p.  387,  36).  Some  of  the  cochlear  fibres  pass  both  ventral 
and  dorsal  nuclei  to  end  in  the  superior  olivary  and  trapezoid 
nuclei.  Axones  from  the  cells  of  these  nuclei  also  join  the  lateral 
fillet. 

The  neurones  of  the  vestibular  nerve  have  their  cell  bodies  situ- 
ated in  Scarpa's  ganglion  (vestibular  ganglion).  These  cells  are 
bipolar,  their  peripheral  processes  ending  freely  among  the  hair  cells 
of  the  crista  and  macula  acustica,  their  central  processes  forming  the 
already  mentioned  vestibular  root.  The  axones  of  the  cells  of  the 
terminal  nuclei  of  the  vestibular  root  form  secondary  vestibular  tracts, 
some  axones  going  to  the  cerebellum  and  midbrain,  others  descending 
in  the  reticular  formation,  still  others  forming  part  of  the  posterior 
longitudinal  fasciculus. 

32.  The  root  fibres  of  the  seventh  (facial)  cranial  nerve  (Fig.  247, 
VII)  and  its  nucleus  of  origin  (Nvii).  These  can  be  seen  in  higher 
sections  of  this  level.      (For  details  see  p.   386,  32.) 

33.  The  root  fibres  of  the  sixth  (abducens)  cranial  nerve  (Fig. 
247,   17)  and  its   nucleus   of  origin.      ( For  details  see   p.   386,  33). 

34.  The  acoustic  striae ;  in  the  lateral  part  of  the  floor  of  the 
fourth  ventricle.  These  are  fibres  of  the  secondary  cochlear  tract 
from  the  dorsal  cochlear  nucleus  (see  p.  381,  31). 

$j.  Transverse  fibres  of  the  pons  Varolii ;  crossing  ventral  to  the 
pyramids  (see  p.  386,  35). 

37.    The  central  tegmental  tract  (see  37,  p.  387). 

6.  Transverse  Section  through  the  Exits  of  the  Root  Fibres  of 
the  Sixth  (Abducens)  and  Seventh  (Facial)  Cranial  Nerves. 

The  following  structures  seen  in  the  preceding  level  have  now 
disappeared  : 

2.  The  lateral  columns  as  such ;  Govvers'  and  von  Monakow's 
tracts  here  lying  in  the  ventral  part  of  the  tegmentum  between  the 
fillet  and  the  root  of  the  seventh  nerve. 

18.   The  arciform  nucleus. 


THE  NERVOUS  SYSTEM. 


385 


22.  The  external  arcuate  fibres;  unless  the  superficial  transverse 
pons  fibres  be  classed  as  arcuate  fibres. 

23.  The  restiform   body;   now  passed   or  passing  into  the   cere- 
bellum as  its  inferior  peduncle. 

24.  The  olivary  nucleus. 

31.    The  cochlear  portion  of  the  auditory  nerve  with  its  nuclei. 
34.   The  acoustic  striae. 

Vllg 


VELt 


w^ 


FIG.  249 — Transverse  Section  of  the  Medulla  through  the  Exits  of  the  Sixth  and  Seventh 
Cranial  Nerves.  (Dejerine).  3,  Pyramid  ;  4,  gelatinous  substance  of  Rolando  and  re- 
mains of  posterior  horn  ;  SR,  reticular  formation  ;  R//i,  fillet  ;  /j,  spinal  root  of  fifth 
nerve  ;  2/,  posterior  longitudinal  fasciculus  ;  23,  restiform  body  or  inferior  cerebellar 
peduncle;  25,  fourth  ventricle;  VIIIv,  vestibular  root  of  eighth  cranial  nerve;  Nvii, 
nucleus  of  origin  of  seventh  cranial  nerve;  VII7,  root  fibres  of  seventh  nerve  passing 
from  nucleus  of  origin  to  floor  of  fourth  ventricle  ;  VUg,  transversely  cut  bundle  of  root 
fibres  of  seventh  nerve  ascending  in  floor  of  fourth  ventricle  ;  IV/,  root  fibres  of  seventh 
nerve  leaving  medulla  ;  Nvi,  nucleus  of  origin  of  sixth  cranial  nerve;  IV,  root  fibres  of 
sixth  cranial  nerve  ;  33  bi,  superficial  transverse  fibres  of  the  pons  ;  33  b2,  deep  transverse 
fibres  of  pons;  j5,  lateral  lemniscus  ;  Pec,  central  tegmental  tract  ;  Xci,  nucleus  of  the 
reticular  formation  ;  Arp,  pontile  nuclei ;  TV,  trapezoid  body  ;  r,  median  raphe  ;  38,  supe- 
rior olivarv  nucleus. 


The  following  structures  are  still  present : 

?.   The  tracts  of  Gowers  and  von  Monakow. 

3.  The  pyramid;   now  occupying  the  middle  of  the  pons. 

4.  The  remains  of  the  posterior  horn. 

7.   The  reticular  formation  (SR) ;   in  which  are  several  groups  of 
ganglion  cells,  the  nuclei  of  the  reticular  formation  (Net). 
12.  The  internal  arcuate  fibres;   rather  indefinite. 
14.    The  fillet  (A?///),  now  called  the  median   lemniscus  to  distin- 
2  5 


;86 


THE   ORGANS. 


guish  it  from  the  lateral  lemniscus ;  much  flattened  dorso-ventrally 
lying  between  the  reticular  formation  and  the  pons. 

15.  The  spinal  root  of  the  fifth  cranial  nerve;  usually  broken  up 
into  several  bundles. 

21.  The  posterior  longitudinal  fasciculus;  now  a  distinctly  sepa- 
rate bundle  lying  next  the  median  line  near  the  floor  of  the  fourth 
ventricle. 

25.  The  fourth  ventricle;  the  roof  now  being  formed  by  the 
cerebellum. 

31.  The  root  fibres  of  the  vestibular  division  of  the  eighth  nerve. 

32.  The  root  fibres  of  the  seventh  (facial)  cranial  nerve  and  its 
nucleus  of  origin.     The  latter  consists  of  a  fairly  well-defined  group 

of  large  motor  cells  situated 
deep  in  the  reticular  formation 
(Fig.  249,  Nvii). 

The  axones  of  the  cells  of 
this  nucleus  pass  dorsally  and 
mesially  toward  the  floor  of  the 
fourth  ventricle  (VII '7).  Here 
they  turn  and  ascend  in  the 
floor  of  the  fourth  ventricle — 
appearing  in  the  section  as  a 
bundle  of  transversely  cut  fibres 
(  VII  g) — to  the  genu  or  bend, 
where  they  turn  ventro-laterally 
and  pass  to  the  surface  (171). 

(Only  portions  of  the  course 
of  the  root  fibres  of  this  nerve 
can  be  seen  in  any  one  section.) 
33.  The  root  fibres  of  the 
sixth  (abducens)  cranial  nerve 
and  its  nucleus  of  origin.  The 
nucleus  consists  of  a  group  of 
large  motor  cells  lying  in  the 
floor  of  the  fourth  ventricle  (Nvi),  partially  surrounded  by  the  genu 
of  the  seventh  nerve.  From  this  nucleus,  fibres  may  be  seen  (  VI), 
passing  ventrally  through  the  reticular  formation  and  pons  to  the 
surface. 

35.   The  pons  Varolii.      This  occupies  the  ventral  part  of  the  sec- 


r///> 


y/' 


FIG.  250.— Diagram  of  Origin  of  Sixth  and 
Seventh  Cranial  Nerves.  (Schafer.)  pyr, 
Pyramid  ;  cr,  restiform  body  ;  dV,  spinal  root 
of  fifth  nerve;  Ventr.IV,  fourth  ventricle; 
VIII v,  vestibular  root  of  eighth  nerve; 
n.  VI,  chief  nucleus  of  sixth  nerve  ;  n'  VI,  ac- 
cessory nucleus  of  sixth  nerve;  /'/,  sixth 
nerve  ;  ;/.  VII,  nucleus  of  seventh  nerve,  from 
which  the  axones  pass  dorso-mesially  to  the 
floor  of  the  ventricle,  where  they  turn  brain- 
ward,  appearing  as  a  bundle  of  transversely 
cut  fibres,  aVII,  and  ascend  to  the  "genu," 
K,  where  they  turn  ami  pass  ventro-laterally 
to  the  surface  as  the  seventh  nerve,  VII. 


THE  NERVOUS  SYSTEM.  387 

tion.  It  consists  of  longitudinal  fibres,  transverse  fibres,  and  gray 
matter  (pontile  nuclei). 

(a)  The  pontile  nuclei  (Np)  are  masses  of  gray  matter  lying 
among  the  fibres  of  the  pons.  They  are  nuclei  of  origin  of  the 
transverse  pontile  fibres. 

{b)  The  transverse  pontile  fibres,  or  midlde  peduncle  of  the  cere- 
bellum, connect  the  pontile  nuclei  with  the  opposite  cerebellar  hemi- 
sphere. They  are  divided  by  the  longitudinal  fibres  into  (In), 
superficial  transverse  fibres  and  (#2)  deep  transverse  fibres. 

(c)  The  longitudinal  fibres  of  the  pons  lie  with  the  pyramidal 
tracts  between  the  superficial  and  deep  transverse  fibres.  They  are 
mainly  descending  axones  to  the  pontile  nuclei  from  cells  situated  in 
the  cerebral  cortex. 

37.  The  central  tegmental  tract  {Fee)  lies  in  the  reticular  forma- 
tion between  the  root  fibres  of  the  sixth  and  seventh  nerves.  It  is 
probably  a  descending  tract  from  higher  centres  to  the  olives. 

The  following  new  structures  are  to  be  noted  : 

36.  The  lateral  lemniscus  or  lateral  fillet  lies  to  the  outer  side  of 
the  reticular  formation.  It  contains  a  mass  of  gray  matter  known  as 
the  nucleus  of  the  lateral  lemniscus.  Its  fibres  are  mainly  a  sec- 
ondary cochlear  tract,  the  axones  of  cells  in  the  terminal  nuclei  of 
the  cochlear  nerve  (see  p.  381,  31).  The  fibres  of  the  lateral  lem- 
niscus terminate  mainly  in  the  gray  matter  of  the  anterior  and  pos- 
terior corpora  quadrigemina,  most  of  them  in  the  corpora  quadri- 
gemina  of  the  same  side,  a  few  in  the  corpora  quadrigemina  of  the 
opposite  side.  Some  fibres  of  the  lateral  lemniscus  probably  pass 
both  anterior  and  posterior  corpora  quadrigemina,  to  end  in  the  cor- 
tex of  the  temporal  lobe. 

38.  The  superior  olive  is  a  mass  of  gray  matter  lying  just  lateral 
to  the  central  tegmental  tract.  This  nucleus,  together  with  several 
other  nuclei  in  its  immediate  vicinity  (pre-olivary  nucleus,  semi- 
lunar nucleus,  and  trapezoid  nucleus)  are  terminal  nuclei  for  the  sec- 
ondary cochlear  fibres  of  the  trapezium  (7>).  Some  of  the  trans- 
verse fibres  passing  through  the  ventral  part  of  the  tegmentum  are 
the  decussating  fibres  of  the  secondary  acoustic  tract  (see  page  384) 
to  the  lateral  fillet. 


388 


THE   ORGANS. 


7.  Transverse  Section  Through  the  Exit  of  the  Root  Fibres  of 
the  Fifth  (Trigeminus)  Cranial  Nerve  (Fig.  251). 

The  following  structures  seen  in  the  last  section  have  disappeared  : 

4.   The  posterior  horn,  which  has   been  serving  as  the  nucleus  of 

termination  for  the  descending  root  of  the  fifth  nerve.     In  some  of 


cerebellum 

Nrt 
FlG.  251. — Transverse  Section  of  the  Medulla  through  the  Exit  of  the  Fifth  Cranial  Nerve. 
(Dejerine.)  3,  Pyramidal  fibres  and  longitudinal  pontile  fibres;  67?,  reticular  formation  ; 
Rm,  fillet;  Tr,  trapezoid  body;  sj,  spinal  root  of  fifth  nerve;  21,  posterior  longitudinal 
fasciculus  ;  2j,  fourth  ventricle  ;  jjl>,  transverse  pontile  fibres  ;  jj  bi,  superficial  transverse 
pontile  fibres  ;  j;  l>2,  deep  transverse  pontile  fibres  ;  Fee,  central  tegmental  tract;  Nrt, 
nucleus  of  the  reticular  formation  ;  Np,  pontile  nuclei  ;  jS,  superior  olivary  nucleus  ;  /', 
root  fibres  of  fifth  cranial  nerve;  NVs,  sensory  nucleus  of  fifth  cranial  nerve;  NVm, 
motor  nucleus  of  fifth  cranial  nerve;  Nft,  nucleus  funiculi  teretis  ;  23,  inferior  cerebellar 
peduncle,  the  continuation  of  the  restiform  body  ;  40,  superior  cerebellar  peduncle;^/', 
transverse  pontile  fibres  forming  middle  cerebellar  peduncle  ;  Lip,  middle  lobe  of  cere- 
bellum ;  -V,  fibres  passing  to  superior  cerebellar  peduncle. 


the  lower  sections  of  this  level  a  small  remnant  of  the  posterior  horn 
may  be  present. 

3  1     The  root  fibres  of  the  vestibular  division  of  the  eighth  cranial 
nerve. 

32.  The  root  fibres  and  nucleus  of  the  seventh  cranial  nerve. 

33.  The  root  fibres  and  nucleus  of  the  sixth  cranial  nerve. 


The   following   structures   seen  in  the  preceding   section  are  still 
present : 


THE  NERVOUS   SYSTEM.  3 §9 

2.  The  tracts  of  Gowers  and  von  Monakow;  not  distinguishable 
in  the  sections,  but  lying  in  the  ventral  part  of  the  tegmentum  just 
internal  to  the  root  of  the  fifth  nerve. 

3.  The  pyramid;  now  much  broken  up  into  bundles  by  the  trans- 
verse fibres  of  the  pons  (35  b). 

7.  The  reticular  formation  {SR) ;  occupies  a  considerable  portion 
of  the  tegmentum,  its  gray  matter  being  known  as  the  nucleus  of  the 
reticular  formation  (AW). 

12.   Internal  arcuate  fibres;   crossing  the  median  raphe. 

14.  The  fillet  (Rm)  ;  much  flattened  dorso-ventrally,  and  broken 
up  into  several  bundles  of  fibres,  which  lie  just  ventral  to  the  reticu- 
lar formation  and  dorsal  to  the  deepest  of  the  transverse  pontile 
fibres. 

15.  The  spinal  root  of  the  fifth  nerve  (see  p.  374,  15). 
21.   The  posterior  longitudinal  fasciculus. 

25.  The  fourth  ventricle;  somewhat  narrower  as  it  is  approach- 
ing the  iter. 

35.  The  pons;    much   increased  in  extent.      (For  details  see  p. 

386,  35-) 

36.  The  lateral  lemniscus.      (For  details  see  p.   3S7,  36.) 

37.  The  central  tegmental  tract  {Fee) ;  in  about  the  same  position. 

38.  The  superior  olive ;   smaller  than  in  the  last  section. 

Note  the  following  new  structures : 

39.  The  root  fibres  of  the  fifth  cranial  nerve  (trigeminus).  As 
the  fifth  is  a  mixed  nerve,  some  of  these  fibres  are  sensory,  others 
motor. 

{a)  The  fibres  of  the  sensory  root  pass  between  the  fibres  of  the 
pons  to  the  floor  of  the  fourth  ventricle,  where  some  of  them  termi- 
nate in  the  main  sensory  nucleus  {NVs),  while  others  turn  spinal- 
ward  as  the  descending  spinal  root  (75),  which  with  its  nucleus 
(the  remains  of  the  posterior  horn)  has  been  noted  in  all  sections  of 
the  medulla. 

(//)  The  fibres  of  the  motor  root  leave  the  medulla  just  internal 
to  those  of  the  sensorv  root.  They  are  axones  of  cells  situated  in 
two  nuclei — only  one  of  which  {NVm)  can  be  seen  in  this  section 
— lying  in  the  lateral  part  of  the  reticular  formation. 

The  cell  bodies  of  the  neurones  whose  axones  make  up  the  sen- 
sory root  of  the  fifth  nerve  are  situated  in  the  Gasserian  or  semilunar 


39° 


THE  ORGANS. 


ganglion.  This  ganglion  is  analogous  to  the  posterior  root  ganglion 
of  the  spinal  nerve.  The  cells  are  unipolar,  the  single  process  bifur- 
cating as  in  the  cells  of  the  spinal  ganglia.  Their  peripheral 
branches  pass  to  the  surface.  Their  central  branches  pierce  the 
fibres  of  the  pons  and,  reaching  the  floor  of  the  fourth  ventricle, 
bifurcate.  The  shorter  ascending  arms  terminate  in  the  main  sen- 
sory nucleus  of  the  fifth  nerve.     The  long  descending  arms  form  the 


FlG.  252.  — Diagram  of  Origin  of  Fifth  Cranial  Nerve.  (Schafer.)  G,  Gasserian  ganglion  ;  a,  <\ 
c,  the  three  divisions  of  the  nerve  ;  m.n.  V,  principal  motor  nucleus  ;  f.s.ii.  V,  principal  sen- 
sory nucleus;  d.s.n.V,  descending  sensory  or  spinal  nucleus;  d.s.l',  descending  or  spinal 
root ;  c.  V  and  c'.V,  secondary  trigeminal  tracts  (axones  of  cells  in  sensory  nuclei);  r, 
median  raphe. 


descending  or  spinal  root  of  the  fifth  nerve.  The  fibres  of  this  root 
send  collaterals  into,  and  terminate  in,  the  gelatinous  substance  of  the 
posterior  horn,  which  thus  constitutes  an  extended  terminal  nucleus 
for  this  root  (Fig.  252). 

The  cell  bodies  of  the  neurones  whose  axones  constitute  the 
motor  root  of  the  fifth  nerve  are  situated,  as  already  noted,  in  two 
nuclei.  One  of  these,  the  principal  motor  nucleus,  has  been  de- 
scribed. The  other  nucleus  consists  of  a  long  column  of  cells  ex- 
tending from  this  level  upward  to  the  region  of  the  corpora  quadri- 
gemina.      The  axones   from  this  nucleus  form  the  descending  motor 


THE  NERVOUS  SYSTEM.  391 

or  mesencephalic  root  of  the  fifth  nerve  (Fig.  253,  Vd).  The  axones 
from  these  two  nuclei  join  to  form  the  motor  root  of  the  fifth  nerve. 
40.  All  three  of  the  cerebellar  peduncles  can  be  seen  in  this  sec- 
tion. The  inferior  peduncle  (23)  is  the  continuation  into  the  cere- 
bellum of  the  restiform  body  which  has  been  noted  in  all  of  the 
sections  above  the  pyramidal  decussation.  (For  details  see  p.  380, 
23.)  The  middle  peduncle  (35  b)  has  been  described  in  connec- 
tion with  the  transverse  fibres  of  the  pons  (see  p.  387,  35  b). 
The  superior  peduncles  (40)  form  a  large  part  of  the  lateral  wall  of 
the  fourth  ventricle.  They  are  more  conspicuous  in  the  succeeding 
section.     (For  details  see  p.  393,  40.) 

THE  MIDBRAIN— MESENCEPHALON  OR  ISTHMUS. 

Through  the  midbrain  can  be  followed  the  further  continuation 
upward  of  the  main  fibre  tracts  of  the  cord  and  medulla.  Ventrally 
the  midbrain  shows  a  deep  groove  or  sulcus,  caused  by  the  diver- 
gence of  the  crusta  or  continuation  of  the  main  motor  tracts.  The 
dorsal  surface  of  the  midbrain  presents  four  rounded  prominences, 
the  two  posterior  and  the  two  anterior  corpora  quadrigemina.  Just 
dorsal  to  the  crusta  is  a  layer  of  gray  matter  which  contains  deeply 
pigmented  nerve  cells.  This  is  known  as  the  substantia  nigra  and 
separates  the  crusta  from  the  rest  of  the  midbrain,  the  parts  dorsal 
to  the  substantia  nigra  being  collectively  known  as  the  tegmentum. 
There  are  thus  to  be  considered  in  studying  the  midbrain,  the  crusta, 
the  tegmentum,  and  the  intervening  substantia  nigra. 

Transverse  Section   of   the  Midbrain  through  the   Exit   of   the 
Fourth  Cranial  Nerve  (Pathetic)  (Fig.  253). 

The  following  structures  present  in  the  preceding  sections  have 
disappeared  : 

12.  The  internal  arcuate  fibres;  unless  the  decussating  fibres  of 
the  superior  peduncles  of  the  cerebellum  be  regarded  as  such. 

15.  Spinal  root  of  the  fifth  nerve;  with  its  nucleus,  the  posterior 
horn. 

25.  The  fourth  ventricle;  now  become  the  iter,  the  roof  of  which 
is  formed  by  the  valve  of  Vieussens  or  anterior  medullary  vellum. 

35.  The  pons. 


392 


THE   ORGANS. 


3/ '.   The  central  tegmental  tract;  no  longer  distinguishable. 

38.  The  superior  olivary  and  trapezoid  nuclei. 

39.  The  fifth  nerve,  with  its  roots  and  nuclei,  excepting  the 
small  descending  motor  (mesencephalic)  root  (Vd),  and   its  nucleus. 

The  following  structures  seen  in  the  preceding  section  are  still 
present : 

In  the  crusta : 

3.  The  pyramid  ( VP).  The  numerous  bundles  of  pyramidal 
fibres  seen  in  the   last   section  among  the   transverse  pontile  fibres 


_NR1 


Fig.  253. — Transverse  Section  of  the  .Midbrain  through  the  Exit  of  the  Fourth  Cranial  Nerve. 
(Oejerine.)  V '  P,  Pyramid;  7,  reticular  formation;  Rm,  fillet;  21,  posterior  longitudinal 
fasciculus;  2y,  iter;  jb,  lateral  lemniscus;  NRl,  nucleus  of  lateral  lemniscus;  I'd,  de- 
scending or  mesencephalic  root  of  fifth  nerve  ;  40,  superior  cerebellar  peduncle  ;  40  a,  dor- 
sal decussation  of  superior  peduncles  ;  40  /»,  ventral  decussation  of  superior  peduncles  ;  AV, 
lateral  nucleus,  a  band  of  gray  matter  lying  between  the  superior  peduncles  and  the 
fillet  ;  L)i,  substantia  nigra  ;  IV,  root  fibres  of  fourth  cranial  nerve;  xIV,  decussation  of 
root  fibres  of  fourth  cranial  nerve;  x,  gray  matter  forming  floor  of  iter;  xF,  tegmental 
decussation. 


now  form  one  large  bundle,  the  crusta.  The  middle  three-fifths  of 
the  latter  are  occupied  by  the  pyramidal  tracts  proper  (cerebro- 
spinal), including  fibres  to  the  motor  nuclei  of  the  cranial  nerves; 
the  mesial  fifth,  mainly  by  axoncs  passing  from  cells  in  the 
frontal  lobe  to  terminate  in  the  pontile  nuclei  ;  the  lateral  fifth,  by 
fibres  which  probably  connect  the  temporal  lobe  with  the  pontile 
nuclei. 


THE  NERVOUS  SYSTEM.  393 

In  the  most  dorsal  part  of  the  crusta  are  a  small  number  of  fibres 
which  have  been  described  as  derived  from  the  fillet  and  as  probably 
passing  either  to  the  cortex  or  thalamus. 

In  the  tegmentum : 

2.  Govvers'  tract  and  von  Monakow's  bundle.  A  part  of  the 
former  has  passed  into  the  cerebellum.  The  part  to  the  thalamus 
lies  in  the  ventral  part  of  the  lateral  lemniscus.  Von  Monakow's 
bundle  lies  just  dorsal  to  the  fillet. 

7.  The  reticular  formation ;  much  diminished  in  size  and  con- 
taining among  other  fibres  ascending  axones  from  cells  of  the  fifth 
nerve  nuclei  (secondary  trigeminal  tract). 

14.  The  fillet;  now  a  much  flattened  band  of  fibres  just  dorsal  to 
the  substantia  nigra. 

21.  The  posterior  longitudinal  fasciculus;  just  ventral  to  the 
gray  matter  of  the  floor  of  the  iter. 

36.  The  lateral  lemniscus;  occupying  with  its  nucleus  (XRI) 
the  extreme  dorso-lateral  part  of  the  tegmentum. 

39  b.  (  Vd)  The  descending  motor  or  mesencephalic  root  of  the 
fifth  nerve.      (For  details  see  p.  390.) 

40.  The  superior  cerebellar  peduncles  or  brachia  conjunctiva. 
These  occupy  the  greater  part  of  the  tegmentum  and  can  be  seen 
decussating  in  the  median  line.  They  are  composed  mainly  of  ax- 
ones from  cells  in  the  dentate  nucleus  and  probably  in  other  cere- 
bellar nuclei.  Crossing  to  the  opposite  side  in  the  decussation, 
these  axones  terminate  mainly  in  the  red  nucleus.  There  are 
probably  also  axones  in  the  superior  peduncles,  which  come  from 
cells  situated  in  higher  centres  and  which  terminate  in  the  cere- 
bellum. 

Of  new  structures,  the  only  ones  to  which  special  attention  is 
called  are : 

41.  The  fourth  cranial  nerve  (pathetic).  The  root  fibres  of  this 
nerve  are  seen  decussating  in  the  roof  of  the  iter  {xIV).  Some 
transversely  cut  bundles  of  fourth  root  fibres  can  also  be  seen  in  the 
lateral  wall  of  the  iter. 

The  fibres  of  this  nerve  are  axones  of  a  group  of  cells  which  lie 
deep  in  the  central  gray  matter.  These  axones  pass  first  dorso-later- 
ally  to  about  the  position  of  the  mesencephalic  root  of  the  fifth  nerve 
when  they  turn   and  run  spinalward.      At   the   level  of  the  anterior 


394 


THE   ORGANS. 


medullary  velum  they  turn  dorso-mesially  to  form  the  above-men- 
tioned decussation,  after  which  they  pass  to  the  surface. 

42.   The  substantia  nigra  (see  general  description,  p.  391). 

Transverse  Section  of  the  Midbrain  through  the  Exit  of  the 
Third  Cranial  Nerve  (Oculomotor)  (Fig.  294). 

The  following  structures  seen  in  the  preceding  section  have  dis- 
appeared : 

39  b.  The  descending  motor  (mesencephalic)  root  of  the  fifth 
nerve. 

41.   The  fourth  cranial  nerve. 

The  following  structures  are  still  present : 

2.  Gowers'  tract  near  lateral  surface;  those  fibres  which  pass  to 
the  anterior  corpus  quadrigeminum. 


FlG.  254.— Transverse  Section  of  the  Midbrain  through  the  Exit  of  the  Third  Cranial  Nerve. 
(Dejerine.)  j,  Pyramid;  7,  reticular  formation  of  tegmentum;  /y,  fillet,  /•"//,  posterior 
longitudinal  fasciculus  ;  2,-,  iter  ;  j\  lateral  lemniscus  :  not  marked,  but  lying  just  dorsal 
to  most  dorsal  fillet  fibres,  //,•  40,  superior  cerebellar  peduncle;  Ln,  substantia  nigra; 
a,  a,  anterior  corpora  quadrigemina  ;  l>,  brachium  of  anterior  corpus  quadrigeminum; 
Cgi,  internal  geniculate  body  ;  ./_?,  red  nucleus;  x,  central  gray  matter  ;  /-'cop,  lateral  gray 
matter  of  tegmentum  (superior  lateral  nucleus  of  Flechsig);  xF,  ventral  tegmental  de- 
cussation or  decussation  of  Forel  ;  xAI,  dorsal  tegmental  decussation  or  decussation  of 
Meynert  ;  .\7//,  nucleus  o£  origin  of  third  cranial  nerve  ;  ///,  root  fibres  of  third  nerve. 

3.   The   crusta;   its   fibres   being  arranged   essentially   as   in    the 
preceding  section. 


THE  NERVOUS  SYSTEM.  395 

7.   The  reticular  formation;   less  extensive. 

14.    The  fillet;   just  dorsal  to  the  substantia  nigra. 

21.  The  posterior  longitudinal  (Flp)  fasciculus ;  not  easily  dis- 
tinguished, but  lying  to  the  ventral  and  lateral  side  of  the  nucleus  of 
the  third  nerve. 

36.  The  lateral  lemniscus;  smaller  from  loss  of  fibres,  which 
ended  in  the  posterior  corpus  quadrigeminum.  The  remainder  of 
its  fibres  pass  upward  to  terminate  in  the  anterior  corpus  quadrigem- 
inum and  in  the  lateral  geniculate  body. 

40.  The  superior  cerebellar  peduncles;  their  decussation,  now 
completed,  lie  one  on  either  side  of  the  median  line. 

42.  The  substantia  nigra  (Lu),  between  the  crusta  and  tegmentum. 

The  following  new  structures  are  to  be  noted  : 

43.  The  anterior  corpora  quadrigemina  (a,  a).  (For  description 
see  p.  396.) 

44.  The  geniculate  bodies,  only  the  medial  of  which  {Cgi)  can 
be  seen  in  the  section;  two  masses  of  gray  matter,  lying,  the  mesial 
just  dorsal,  the  lateral,  dorso-lateral  to  the  crusta.  The  lateral  genic- 
ulate bodies  are  connected  with  the  optic  tracts  (see  Optic  Nerve, 
p.  426). 

45.  The  red  nucleus;  a  large  mass  of  gray  matter  lying  between 
the  substantia  nigra  and  the  posterior  longitudinal  fasciculus  just  to 
the  outer  side  of  the  root  fibres  of  the  third  nerve.  The  relation  of 
this  nucleus  to  the  superior  peduncles  of  the  cerebellum  was  de- 
scribed in  connection  with  the  preceding  section  (p.  393,  40).  From 
cells  in  this  nucleus  axones  pass  upward  to  higher  centres  and  down- 
ward (von  Monakow's  bundle)  to  the  spinal  cord. 

46.  The  root  fibres  and  nucleus  of  origin  of  the  third  cranial 
nerve  (oculomotor).  The  nucleus  is  a  well-defined  group  of  large 
motor  cells  lying  in  the  deepest  part  of  the  central  gray  matter. 
From  this  nucleus,  bundles  of  fibres  may  be  seen  passing  in  a  curved 
course  through  the  reticular  formation  to  reach  the  surface  just  to 
the  inner  side  of  the  crusta  {III). 

The  Corpora  Quadrigemina.  —  The  Posterior  Corpora  Quadrigem- 
ina.— These  consist  mainly  of  gray  matter  and  are  connected  with 
parts  above  and  below  by  tracts  of  fibres.  The  fibres  which  ascend 
to  terminate  in  the  gray  matter  of  the  posterior  corpus  quadrigemi- 
num come  mainly  from   the   lateral  lemniscus  (for  fibres  which  this 


396  THE   ORGANS. 

contains  see  p.  3S7,  36).  From  the  cells  of  the  gray  matter  of 
the  posterior  corpus  quadrigeminum  some  axones  descend  in  the 
lateral  lemniscus;  other  axones  ascend,  joining  the  fibres  of  that  part 
of  the  lateral  lemniscus  which  passes  by  the  posterior  corpus  quadri- 
geminum. These  together  form  the  inferior  brachium  quadrigemi- 
num and  pass  to  the  anterior  corpus  quadrigeminum  and  to  the 
medial  corpus  geniculatum. 

The  Anterior  Corpora  Quadrigemina. —  These  consist  of  both 
gray  matter  and  white  matter.  The  white  matter  is  made  up 
mainly  of  fibres  of  the  optic  tracts,  axones  of  neurones  whose  cell 
bodies  are  located  in  the  retinae.  The  gray  matter  of  the  anterior 
corpora  quadrigemina  serves  as  the  terminal  nuclei  for  these  axones. 
It  also  serves  as  a  terminal  nucleus  for  some  of  the  axones  of  the 
lateral  lemniscus — i.e.,  for  the  secondary  acoustic  tract.  The  neu- 
rones whose  cell  bodies  are  situated  in  the  anterior  corpora  quad- 
rigemina send  their  axones  mainly  downward.  Their  destinations 
are  not  fully  known.  Some  appear  to  cross  through  Meynert's  de- 
cussation (Fig.  254)  to  the  opposite  side,  where  they  continue  spinal- 
ward,  giving  off  collaterals  and  terminals  to  the  nuclei  of  the  third, 
fourth,  and  sixth  cranial  nerves.  Other  axones  pass  downward  on 
the  same  side,  mingling  with  the  fibres  of  the  fillet  and  probably  end 
in  the  pontile  nuclei,  thus  bringing  the  corpora  quadrigemina  into 
connection  with  the  opposite  cerebellar  hemisphere.  Still  other 
axones  from  the  anterior  corpora  quadrigemina  probably  pass  upward 
in  the  tegmentum  to  the  thalamus. 

The  Cerebral  Peduncles  (crura  cerebri). — These  are  the  direct 
continuation  brainward  of  the  crusta  and  tegmentum  (see  sections  of 
midbrain),  the  former  containing  the  main  motor  tract  (p.  392,  3), 
the  latter  containing  the  main  sensory  tract.  As  the  peduncles  ap- 
proach the  basal  ganglia,  the  substantia  nigra  disappears  and  the 
tegmentum  lies  just  dorsal  to  the  crusta.  These  bundles  of  fibres 
pass  through  the  basal  ganglia  between  the  nucleus  caudatus  and  the 
optic  thalamus  on  the  mesial  side,  and  the  nucleus  lenticularis  on  the 
lateral  side.  Here  they  form  the  internal  capsule,  which  is  directly 
continuous  above  with  the  corona  radiata  through  which  the  fibres 
enter  the  cortex  cerebri.  In  a  horizontal  section  through  the  basal 
ganglia,  the  internal  capsule  is  seen  to  present  a  sharp  bend  ox  genu 
somewhat  anterior  to  its  mid-point.  This  bend  divides  the  capsule 
into  an  anterior  portion  and  a  posterior  portion.     The  anterior  portion 


THE  NERVOUS  SYSTEM.  397 

lies  between  the  caudate  nucleus  internally  and  the  lenticular  nucleus 
externally.  This  part  of  the  capsule  consists  mainly  of  fibres  which 
connect  the  cortex  cerebri  and  the  optic  thalamus.  The  posterior 
portion  of  the  internal  capsule  lies  between  the  lenticular  nucleus  on 
its  outer  side  and  the  optic  thalamus  on  its  inner  side.  About  the 
anterior  two-thirds  of  this  portion  is  occupied  by  the  fibres  of  the 
pyramidal  tract  (including  descending  fibres  to  the  motor  cranial 
nerve  nuclei). 

THE    CEREBELLUM. 
General  Histology  of  the  Cerebellar  Cortex. 

The  cerebellum  consists  of  a  central  portion  or  core  of  white  mat- 
ter which  extends  outward  into  the  cortex  as  a  seiies  of  transversely 
disposed  branching  plates.  These,  covered  by  a  layer  of  gray  mat- 
ter, form  the  lamina,  which  can  be  seen  on  the  surface,  and  which  on 
transverse  section  present  the  characteristic  leaf-like  appearance 
known  as  the  arbor  vitce. 

Each  leaflet  is  seen  on  section  to  consist  of  (i)  a  central  core  of 
white  matter  and  (2)  a  covering  of  gray  matter  which  consists  of 
three  layers  :  (a)  an  internal  or  granular  layer,  (/?)  an  external  or 
molecular  layer,  and  between  these  (c)  a  layer  composed  of  a  single 
row  of  very  large  cells,  the  layer  of  Purkinje  cells. 

(i)  The  white  matter  consists  of  medullated  nerve  fibres  which 
pass  out  in  a  radial  manner  into  the  layers  of  gray  matter.  These 
fibres,  while  apparently  alike,  maybe  subdivided  into  (a)  fibres  which 
are  axones  of  cells  situated  in  other  parts  of  the  nervous  system — 
these  axones  are  passing  to  their  terminations  in  the  cerebellar  cor- 
tex; (/;)  fibres  which  are  axones  of  cells  situated  in  the  cerebellum 
(mainly  axones  of  cells  of  Purkinje) — these  axones  pass  through  the 
white  matter  of  the  cerebellum  to  terminate  in  some  other  part  of 
the  nervous  system  ;  (c)  fibres  which  are  axones  of  neurones  entirely 
confined  to  the  cerebellum. 

(2)  The  gray  matter,  or  cortex  ccrebelli,  may  be  subdivided  into: 
(a)  an  internal,  granular  or  nuclear  layer;  (//)  an  outer  molecular 
layer,  and  between  the  two,  (c)  the  layer  of  Purkinje  cells. 

(a)  The  internal,  granular,  or  nuclear  layer  appears  under  ordinary 
staining  methods  to  be  composed  of  a  mass  of  small,  closely  packed 
cells,  each  consisting  of  a  nucleus   surrounded  by  a  small  amount 


;98 


THE   ORGANS. 


of  protoplasm  (Fig.  255).  Intermingled  with  these  cells  are  meclul- 
lated  and  non-medullated  nerve  fibres.  Studied  by  the  method  of 
Golgi,  the  nerve-cell  elements  of  this  layer  can  be  divided  into  (1) 
small  granule  cells  and  (2 )  large  granule  cells.     The  small  granule 


FIG.  255 —From  Section  through  the  Cerebellar  Cortex,  Stained  with  Haematoxylin-eosin. 
( Boh m  and  von  Davidoff.)  /,  Hlood-vessel  ;  2,  dendrite  of  Purkinje  cell  ramifying  in  mo- 
lecular layer  ;  _?,  body  of  Purkinje  cell  at  junction  of  molecular  and  granular  layers;  ./ 
and  j-,  cells  of  the  granular  layer  ;  6,  layer  of  nerve  fibres  (white  matter). 

cells  (  Fig.  257,  c)  are  multipolar,  their  short  dendritic  processes  rami- 
fying in  the  granular  layer;  their  axones,  which  are  non-medullated, 
passing  into  the  molecular  layer.  Here  each  axone  bifurcates,  the 
branches  running  parallel  to  the  surface  and  to  the  lamina,  and 
terminating  freely.  The  large  granule  cells  (Fig.  257,  <l)  are  also 
multipolar.  Their  dendrites,  however,  pass  outward  to  ramify  in  the 
molecular  layer,  while  their  axones  branch  rapidly  and  form  a  dense 
network  in  the  granular  layer.  The  dense  plexus  of  nerve  fibres  in 
the  granular  layer  is  formed  by  the  processes  of  the  cells  above  de- 
scribed, by  axones  and  their  collaterals  of  Purkinje  cells,  and  by  fibres 
which  enter  the  layer  from  the  central  core  of  white  matter. 
Reaching  the  boundary  between  the  granular  layer  and  the  molecular 


THE  NERVOUS   SYSTEM. 


399 


layer,  many  of  these  fibres  turn  and  pass  horizontally  and  in  a  direc- 
tion transverse  to  the  long  axis  of  the  convolution.  From  these, 
branches  pass  vertically  into  the  molecular  layer. 

(b)  The  molecular  layer  contains  larger  and  smaller  multipolar 
cells.  Most  of  the  dendrites  of  these  cells  pass  toward  the  surface. 
The  axones  run  horizontally  in  the  transverse  axis  of  the  convolution 
(Fig.  257,  b).  A  few  collaterals  pass  upward.  Most  of  the  collat- 
erals and  terminals  pass  downward  to  end  in  basket-like  arborizations 
around  the  bodies  of  the  Purkinje  cells.  For  this  reason  these  cells 
of  the  molecular  layer  are  often  called  "basket  cells."  There  are 
also  found  in  this  layer  cells  the  destination  of  whose  axones  is  un- 
known. The  fibres  of  this  layer  consist  of  processes  of  already  de- 
scribed  cerebellar  cells,  together  with  fibres  which   come  from   the 


FIG.  256.— Cross  Section  of  a  Cerebellar  Convolution  Stained  by  Weigert's  Method.  (Kolli- 
ker.)  m,  Molecular  layer  ;  K,  granular  layer  ;  w,  white  matter  ;  q,  fine  fibres  passing  from 
white  matter  into  the  molecular  layer  ;  tr,  dots  represent  longitudinal  fibres  of  molecu- 
lar layer  among  bodies  of  Purkinje  cells. 


white  matter,  lose  their  medullary  sheaths,  and  end  in  terminal   ar- 
borizations around  the  dendritic  processes  of  the  Purkinje  cells. 

(c)  The  cells  of  Purkinje  (Fig.  257,  a;  Fig.  258,  n;  Fig.  259) 
lie  in  the  molecular  layer  just  at  the  margin  of  the  granular  layer. 
From  the  neck  of  the  cell  pass  off  two  large  dendritic  processes 
which  give  rise  to  an  enormous  number  of  branches.     These  ramify 


4-00 


THE   ORGANS. 


in  the  molecular  layer.  This  ramification  is  not  equally  extensive 
in  all  directions,  but  is  much  greater  in  the  plane  transverse  to  the 
long  axis  of  the  lamina  (compare  Pigs.  258  and  259). 

In  addition  to  the  already  mentioned  basket  network  formed  by 
the  terminals  of  "basket"  cells  around  the   bodies  of  the   Purkinje 


Fig.  257.— From  a  Transverse  Sagittal  Section  of  a  Cerebellar  Convolution  of  a  Rabbit  Seven 
Days  Old.  Golgi  method.  (Dejerine,  after  Retzius.)  ak,  Molecular  layer ;  a,  Purkinje 
cell  ;  to  right  a  Purkinje  cell  the  dendrites  of  which  are  not  included  in  section  ;  af,  ax- 
ones  of  Purkinje  cells,  giving  off  collateral  branches,  afs;  6,  horizontal  cells  of  molecu- 
lar laver,  their  axones,  bf,  running  in  the  transverse  axis  of  the  convolution  (the  col- 
laterals which  pass  downward  from  these  axones  and  form  basket-works  around  the 
bodies  of  the  Purkinje  cells  are  not  impregnated);  c,  cells  of  the  granular  layer  the 
axones  of  which  enter  the  molecular  layer  where  they  turn  and  run  in  the  long  axis  of 
the  convolution,  thus  appearing  as  dots  in  this  section;  d,  large  granule  cell  of  granule 
layer,  its  dendrites  passing  toward  the  molecular  layer,  its  axone,  <//",  branching  rapidly 
and  terminating  in  the  granule  layer  near  its  i  ell  of  origin  ;  a",  another  type  of  small 
granule  cell  ;  ///,  nerve  fibre  terminating  in  pericellular  network  ;  ////and  kf,  nerve  fibres 
terminating  in  the  cerebellar  cortex  ;  e,  neuroglia  cells. 


cells,  networks  of  fibres  from  the  white  matter  terminating  in  the 
cerebellar  cortex  surround  the  larger  dendritic  processes.  These  arc- 
known  as  "climbing"  fibres. 

The  axone  of  the   Purkinje  cell  is  given  off  from  the  side  of  the 


THE  NERVOUS  SYSTEM. 


401 


cell  opposite  to  the  main  dendrite,  and,  becoming  medullated,  enters 
the  white  matter  (Fig.  259,  n). 

Besides  the  gray  matter  of  the  cerebellar  cortex,  isolated  masses 


FIG.  25S.— Diagram  of  Longitudinal  Section  of  Cerebellar  Cortex.  Golgi  method.  (Kolliker.) 
gr,  Cell  of  the  granular  layer  ;  ?z,  axone  of  granule  cell  ;  «',  the  same  in  molecular  layer 
where  it  branches  and  runs  in  long  axis  of  convolution  ;  /,  Purkinje  cell  showing  how 
much  less  extensively  its  dendrites  p')  branch  in  long  axis  of  lamina.    (Compare  Fig.  259.) 

of  gray  matter,  the  cerebellar  nuclei  are  found  in  the  white  matter 
of  the  central  core.  The  largest  of  these  is  the  dentate  nucleus,  an 
irregular  wavy  lamina  somewhat  resembling  the  olive  and  situated  at 


FIG.  259. — Purkinje   Cell   from   Human   Cerebellum  (section  transverse  to  long  axis  of  lam- 
ina).    Golgi  method.     (Kolliker.)     Showing  extent   of  dendritic   branching   in  molecular 
laver.     n,  Axone  ;  k,  collateral. 
26 


4-02 


THE   ORGANS. 


about    the  middle   of   each   cerebellar   hemisphere.      Other    smaller 
nuclei  occur  in  the  white  matter  of  the  middle  lobe. 

The  connections  of  the  cerebellum  with  other  nerve  centres 
through  its  superior,  middle,  and  inferior  peduncles  have  been  de- 
scribed in  connection  with  the  medulla  (page  391,  40). 


THE    CEREBRUM. 
General  Histology  of  the  Cerebral  Cortex. 

Each  cerebral  convolution,  like  the  convolutions  of  the  cerebel- 
lum, consists  of  a  central  white  core  covered  over  by  a  layer  of  gray 
matter,  which  latter  constitutes  the  cortex  cerebri. 


B  A  B 

Fig.  260.— From  Vertical  Section  of  Human  Cerebral  Cortex.  Weigert  stain.  X  10.  De- 
tail drawn  under  a  magnification  of  sixty  diameters.  (Dejerine).  A,  Corona  radiata  or 
central  core  of  white  matter  ;  />',  gray  matter  of  cortex  ;  a,  superficial  tangential  fibres  ; 
d,  deep  tangential  fibres  ;  b  and  c,  intermediate  bands  of  tangential  fibres,  b  sometimes 
known  as  the  outer  line  of  Baillarger,  c,  as  the  inner  line  of  Baillarger  ;  e,  radiation  fibres 
'association,  commissural,  and  projection  fibres);  j\  association  fibres  between  the  two 
adjacent  convolutions. 

The    cortex   cerebri  may  be    divided    into    three    fairly    distinct 
layers:    (a)   an   outer,    barren,    or   molecular   layer,  or  layer   of  few 


THE  NERVOUS   SYSTEM. 


403 


nerve  cells,  (b)  a  middle   layer,  or  layer  of  pyramidal  cells,  and  (c) 
an  inner  layer,  or  layer  of  polymorplious  cells. 

(a)  The  Barren  or  Molecular  Layer  (Fig.  261,  A). — The  nerve 
cells  of  this  layer  are  known  as  the 
cells  of  Cafal.  They  are  fusiform, 
triangular,  or  irregular  in  shape,  and 
both  their  dendrites  and  axones  ram- 
ify in  this  outer  layer,  the  axones 
passing  mainly  in  a  direction  parallel 
to  the  surface.  This  layer  also  con- 
tains the  terminations  of  the  apical 
dendrites  of  the  pyramidal  cells  (Fig. 
261,  a),  some  medullated  nerve  fibres 
running  parallel  to  the  surface  and 
known  as  the  superficial  tangential 
fibres  (Fig.  260,  a),  and  a  rich  plexus 
of  neuroglia. 

(b)  The  Layer  of  Pyramidal  Cells 
(Fig.  261,  B  and  C). — This  is  often 
described  as  two  separate  layers,  an 
outer  layer  of  small  pyramidal  cells 
(B)  and  a  deeper  layer  of  large 
pyramidal  cells  (C).  It  seems  bet- 
ter to  describe  it  as  a  single  layer 
composed  mainly  of  small  pyramidal 
cells,  in  the  deeper  portion  of  which 
the  larger  pyramidal  cells  are  found. 
Each  pyramidal  cell  has  passing  off 
from  its  outwardly  directed  angle  a 
large  apical  or  main  dendrite  (Fig. 
261,  d).  This  dendrite  sends  off 
small  lateral  twigs  and  terminates  in 
numerous  branches  in  the  molecular 
layer.  Smaller  dendritic  processes 
pass  off  from  the  sides  and  base  of 
the  cell.  The  axone  (Fig.  261,  e) 
originates  from  the  base  of  the  cell 
and  enters  the  white  matter  of  the 
corona  radiata.      During   its  passage 


FTG.  261. — From  Vertical  Transverse 
Section  of  Cerebral  Cortex  of  a 
Mouse.  Golgi  method.  (Ramon  y 
Cajal.)  A,  Barren  or  molecular 
layer  ;  B,  layer  of  small  pyramidal 
cells  ;  C,  layer  of  large  pyramidal 
cells  ;  D,  layer  of  polymorphous  cells  ; 
jS1,  white  matter;  a,  dendritic  ramifi- 
cations of  p3Tamidal  cells  showing 
gemmules;  b,  small  superficial  py- 
ramidal cell  ;  c,  axone  of  small  pyram- 
idal cells;  </,  large  pyramidal  cells; 
e,  axone  of  large  pyramidal  cells  ;  f, 
so-called  inverted  pyramid  with  ax- 
one passing  toward  the  surface  ;  g; 
smaller  cells  with  ascending  axones  ; 
hy  axones  within  white  matter  ;  /', 
polymorphous  cell  sending  axone  into 
white  matter  ■,/,  cell  of  Golgi  type  II. 


404 


THE   ORGANS. 


through  the  gray  matter  it  sends  off  collateral  branches.  Some  of 
these  collateral  branches  are  medullated  and  form  some  of  the  deep 
tangential  fibrfs  (Fig.  260,  d).  The  large,  medium  size,  and  small 
cells  are  apparently  identical  in  structure,  differing  from  one  an- 
other mainly  in  size.  Among  the  deeper  cells  of  this  layer  are 
found  some   very   large   pyramidal   cells,    called    the  cells  of  Betz. 


FIG.  262.— From  Vertical  Section  of  Human  Cortex  Cerebri.  Weigert  stain.  (Kolliker.) 
Showing  few  small  pyramidal  cells  and  rich  plexus  of  medullated  nerve  fibres.  The 
bundles  of  fibres  seen  passing  vertically  are  the  bundles  of  radiation  fibres  passing  to 
and  from  the  white  matter. 

These  cells  are  found  only  in  the  motor  cortex,  and  it  is  believed 
that  it  is  the  axones  of  these  cells  which  pass  down  through  the  in- 
ternal capsule  to  the  cord  as  the  main  cortico-spinal  motor  tract. 

In  this  layer  are  also  found  cells — cells  of  Martinotti — (Fig. 
261  ,g)  the  dendrites  of  which  pass  downward,  while  their  axones  pass 
upward  to  the  molecular  layer,  where  they  turn  and  run  parallel  to 
the  surface  as  the  (medullated)  superficial  tangential  fibres. 

Cells  of  Golgi  type  II.  are  also  found  in  this  layer  (Fig.  261,  /). 
Their  axones  branch  rapidly  and  end  in  the  gray  matter  in  the 
vicinity  of  their  cells  of  origin. 


THE  NERVOUS  SYSTEM.  405 

The  fibres  of  this  layer  consist  of  the  axones  and  dendrites  of 
cells  above  described  (some  axones  being  medullated)  and  of  axones 
from  cells  in  other  regions  which  are  passing  to  their  terminations 
(many  of  the  latter  being  medullated). 

(c)  The  cells  of  the  third  layer  (Fig.  261,  D)  are  fusiform  or 
irregular  (polymorphous)  in  shape.  They  have  no  apical  dendrites, 
their  protoplasmic  processes  coming  off  irregularly  and  ramifying 
mainly  in  this  layer.  Their  axones  pass  downward  into  the  white 
matter. 

The  fibres  of  this  layer  consist  of  the  axones  and  dendrites  of 
the  cells  found  in  this  layer,  of  the  axones  of  the  pyramidal  cells 
(now  mostly  medullated),  and  of  axones  of  cells  in  other  parts  of  the 
nervous  system  which  are  passing  to  their  terminations  (most  of 
these  axones  are  medullated). 

The  corona  radiata  (Fig.  260,  A),  or  central  core  of  white  mat- 
ter, consists  of  medullated  nerve  fibres.  These,  upon  reaching  the 
margin  of  the  gray  matter,  radiate  into  the  latter  as  bundles  of  fibres, 
thus  giving  to  the  cortex  a  vertically  striated  appearance.  The 
corona  radiata  consists  of  the  following  fibres,  which,  of  course,  can- 
not be  differentiated  in  Weigert-stained  sections. 

(1)  Descending  axones  of  the  large  and  small  pyramidal  cells  and 
of  the  polygonal  cells  of  the  deep  layer.  These  axones  become 
medullated  and  pass  (a)  to  other  convolutions  of  the  same  hemi- 
sphere— association  fibres  ;  these  may  be  adjacent  convolutions  in  the 
same  lobe  or  distant  convolutions  in  the  same  or  other  lobes ;  (/;) 
through  the  corpus  callosum  to  convolutions  of  the  opposite  hemi- 
sphere— these  are  also  fibres  of  association,  but  are  conveniently  called 
commissural  fibres ;  (c)  to  the  internal  capsule  as  fibres  of  the  de- 
scending tracts — projection  fibres. 

(2)  Ascending  axones  of  cells  situated  in  other  parts  of  the 
nervous  system,  which  are  passing  to  their  terminal  arborizations 
among  the  cells  of  the  cortex  cerebri.  These  fibres  are:  (a)  Axones 
of  cell  bodies  which  are  situated  in  other  convolutions  of  the  same 
hemisphere — association  fibres;  (b)  axones  of  cell  bodies  which  are 
situated  in  the  convolutions  of  the  opposite  hemisphere — these  pass 
through  the  corpus  callosum — commissural  fibres  ;  (c)  axones  which 
have  come  through  the  internal  capsule  from  cells  situated  in  lower 
centres — projection  fibres  ;  these  axones  are  passing  to  their  termi- 
nal arborizations  in  the  cortex. 


4o6 


THE   ORGANS. 


THE  NERVOUS  SYSTEM.  407 

In  addition  to  the  fibres  of  the  corona  radiata,  which  form  dense 
plexuses  among  the  nerve  cells,  are  bundles  of  fibres  which  traverse 
the  gray  matter  at  right  angles  to  the  fibres  of  the  corona.  These 
form  more  or  less  distinct  white  lines,  as  seen  with  the  naked  eye  in 
the  fresh  cortex.  The  outermost  of  these  in  the  molecular  layer  have 
been  mentioned  as  the  superficial  tangential  fibres.  The  deep  tan- 
gential fibres  form  a  second  "white  line"  (known  as  the  outer  line 
of  Baillarger)  just  outside  of  the  layer  of  large  pyramids.  A  third 
white  line  through  the  layer  of  large  pyramids,  the  inner  line  of 
Baillarger,  is  present  in  the  greater  part  of  the  cortex. 

While  the  above-described  arrangement  of  cells  and  fibres  may 
be  considered  to  be  in  general  characteristic  of  the  cerebral  cortex, 
much  variation  exists  in  different  regions. 

TECHNIC. 

(1)  The  general  structure  of  the  cerebellum  is  well  brought  out  by  staining 
sections  of  formalin-Miiller's  fluid-fixed  material  with  haematoxylin-picro-acid-fuch- 
sin  (technic  3,  p.  16),  and  mounting  in  balsam. 

(2)  The  arrangement  of  the  cell  layers  of  both  cerebellum  and  cerebrum,  as 
well  as  certain  details  of  internal  structure  of  the  cells,  can  be  studied  in  sections 

Fig.  263.— Diagram  showing  the  Most  Important  Direct  Paths  which  an  Impulse  follows  in 
passing  from  a  Sensory  Surface  to  the  Cerebral  Cortex  and  from  the  latter  back  to  a  Mus- 
cle ;  also  some  of  the  cranial-nerve  connections  with  the  cerebral  cortex.  A,  Sensory 
cortex  ;  B,  motor  cortex  ;  C,  level  of  third  nerve  nucleus  ;  D,  level  of  sixth  and  seventh 
nerve  nuclei  ;  E,  level  of  sensory  decussation  ;  F.  level  of  pyramidal  decussation  ;  G,  spi- 
nal cord. 

From  Periphery  to  Cortex. 

Neurone  No.  /.—  The  Peripheral  Sensory  Neurone:  i,  Spinal ;  cell  bodies  in  spinal 
ganglia  ;  sensory  end-organ,  S,  peripheral  arm  of  spinal  ganglion  cell  ;  central  arm  of  spi- 
nal ganglion  cell  as  fibre  of  dorsal  root  to  column  of  Goll  or  of  Burdach,  thence  to  nu- 
cleus of  one  of  these  columns  in  the  medulla.  Vx,  Cranial  (example,  fifth  cranial  nerve, 
trigeminus)  ;  cell  bodies  in  Gasserian  ganglion  ;  sensory  end  organ  ;  peripheral  arm  of 
Gasserian  ganglion  cell  ;  central  arm  of  Gasserian  ganglion  cell  to  medulla  as  sensory 
root  of  fifth  nerve,  thence  to  terminal  nuclei  in  medulla. 

Neurone  No.  2. — 2,  Spinal  connection— cell  body  in  nucleus  of  Goll  or  of  Burdach  ;  ax- 
one  passing  as  fibre  of  fillet  to  thalamus.  Vz,  cranial  nerve  connection  (trigeminal),  cell 
bods'  in  one  of  trigeminal  nuclei  in  medulla,  axone  as  fibre  of  secondary  trigeminal  tract 
to  thalamus. 

Neurone  No.  3.-3.  Cell  body  in  thalamus,  axone  passing  through  internal  capsule  to 
termination  in  cortex. 

From  Cortex  to  Periphery. 

Neurone  No.  4. — 4.  Cell  body  in  motor  cerebral  cortex;  axone  through  internal  cap- 
sule and  crusta  to  (a)  motor  nuclei  of  cranial  nerves,  (b)  by  means  of  pyramidal  tracts  to 
ventral  horns  of  spinal  cord. 

Nein-one  No.  5.-5,  Spinal,  Cell  body  in  ventral  horn  of  cord  ;  axone  as  motor  fibre  of 
ventral  root  through  mixed  spinal  nerve  to  muscle. 

Neurone  No. 3.  — Cranial — Jrb,  Cell  body  in  motor  nucleus  of  trigeminus;  axone  pass- 
ing to  muscle  as  motor  fibre  of  fifth  nerve. 

IIIb.  Peripheral  motor  neurone  of  third  nerve— oculomotor.  fYs,  Peripheral  motor 
neurone  of  sixth  nerve — abducens.  f  V/5,  Peripheral  motor  neurone  of  seventh  nerve — 
facial.     -Y7y5,  Peripheral  motor  neurone  of  twelfth  nerve— hypoglossal. 


408 


Fig.  264. 


THE  NERVOUS  SYSTEM.  409 

of  alcohol  or  formalin-fixed  material  stained   by  the  method  of  Nissl  (technic, 
p.  28). 

(3)  The  distribution  of  the  medullated  nerve  fibre  of  either  the  cerebellar  or 
cerebral  cortex  is  best  demonstrated  by  fixing  material  in  Midler's  fluid  (technic  4, 
p.  5)  or  in  formalin-Midler's  fluid,  and  staining  rather  thick  sections  by  the  Wei- 
gert  or  Weigert-Pal  method  (technic,  pp.  25  and  26). 

(4)  The  external  morphology  of  the  cerebellar  and  cerebral  neurones  and  the 
relations  of  cell  and  fibre  can  be  thoroughly  understood  only  by  means  of  sections 
stained  by  one  of  the  Golgi  methods  (technic,  pp.  27  and  28).  Especially  in  the 
case  of  the  cerebellum,  sections  should  be  made  both  at  right  angles,  and  longi- 
tudinal to  the  long  axis  of  the  convolution.  Golgi  preparations  from  embryonic 
material  and  from  the  brains  of  lower  animals  furnish  instructive  pictures. 

Fig.  264.— Diagram  showing  Some  of  the  More  Important  Cerebellar  Connections.  Paths 
which  an  impulse  might  follow  in  passing  from  the  periphery  to  the  cerebral  cortex,  via 
the  cerebellum  and  from  cortex  to  periphery  via  the  cerebellum.  A,  Sensor}'  cortex  ; 
B,  motor  cortex  ;  6',  level  of  red  nucleus;  D,  level  of  pontile  nuclei  ;  E,  level  of  sensory 
decussation  and  olivary  nucleus;  F,  cervical  cord  ;  G,  lumbar  cord  ;  M,  motor  termina- 
tion in  muscle  ;  S,  sensory  termination  in  epithelium  ;  Cer,  cerebellum. 

From  Periphery  to  Cerebellum. 

Neurone  No.  i. — Peripheral  sensory  spinal  neurone— spinal  ganglion  cell  ;  peripheral 
process  ending  in  sensory  end-organ  ;  central  process  ending  :  {a)  after  passing  up  through 
the  column  of  Goll  or  the  column  of  Burdach,  in  the  nucleus  of  the  column  of  Goll  or  in 
the  nucleus  of  the  column  of  Burdach,  in  the  medulla  ;  (b)  in  the  column  of  Clarke  ;  (e)  in 
the  general  gray  matter  of  the  cord  around  column  cells. 

Neurone  No.  2  —2a,  Clarke's  column  cell,  direct  cerebellar  tract  to  vermis  of  cerebellum  ; 

20,  tautomeric  and  heteromeric   cells  of  cord,  tract  of  Gowers  to  vermis  of  cerebellum, 

corpora  quadrigemina  and  thalamus  ;  2.",  tautomeric  cells  of  nuclei  of  columns  of  Goll  and 

of  Burdach  ;  restiform  body  to  vermis  of  cerebellum  ;  2d,  heteromeric  cells  of  nuclei  of 

columns  of  Goll  and  of  Burdach  ;  restiform  body  to  vermis  ;  2c>  (not  marked  with  letter 

on  cut),  heteromeric  cell  of  olivary  nucleus  (spinal    connections  uncertain)  ;  restiform 

bodv  to  cerebellum. 

From  Cerebellum  to  Cerebral  Cortex. 

Neurone  No.  3. — Cells  of  the  cerebellar  cortex,  of  the  dentate  nucleus  and  of  other 
cerebellar  nuclei  ;  superior  cerebellar  peduncles  to  opposite  red  nucleus  and  thalamus. 
Neurone  No.  4.  -  Cells  of  red  nucleus  and  of  thalamus  to  cerebral  cortex. 

From  Cerebral  Cortex  to  Cerebellum. 

Neurone  No.  j.—ja.  Cell  of  frontal  cerebral  cortex  ;  mesial  part  of  crusta  to  pontile 
nuclei  (fronto-pontile  fibres)  ;  jb,  cell  in  temporal  cerebral  cortex  ;  lateral  part  of  crusta 
to  pontile  nuclei  (temporo-pontile  fibres). 

Neurone  No.  6.  — Cells  of  pontile  nuclei;  middle  peduncle  of  cerebellum  (tranverse 
pontile  fibres)  to  opposite  cerebellar  hemisphere. 

From  Cerebellum  to  Periphery. 

Neurone  No.  7.— Cells  in  cerebellum  ;  tract  of  Loewenthal  to  ventral  horn  of  cord. 
Neurone  No.  A— Motor  cells  of  ventral  horn  through  mixed  spinal  nerve  to  muscle  ;  or 
Neurone  No.  7.— Ceils  in  cerebellar  cortex  :  restiform  body  to  opposite  olivary  nucleus 
(cerebello-olivary  fibres). 

Neurone  No.  8.— Cells  in  olivary  nucleus  to  ventral  horn  of  cord  (tract  of  Helweg  ?). 
Neurone  No.  9.— Motor  cell  of  ventral  horn  through  mixed  spinal  nerve  to  muscle. 
Ass'n,  Association  neurone  of  cerebellum. 


410  THE  ORGANS. 

The  Pituitary  Body. 

The  pituitary  body  or  hypophysis  cerebri  consists  of  two  lobes 
which  are  totally  different  both  in  structure  and  in  origin. 

The  Anterior  Lobe. — This  is  the  larger,  and  is  glandular  in 
character.  It  is  of  ectodermic  origin,  developing  as  a  diverticulum 
from  the  primitive  oral  cavity.  Its  mode  of  development  is  that  of 
a  compound  tubular  gland,  the  single  primary  diverticulum  undergoing 
repeated  division  to  form  the  terminal  tubules.  The  original  diver- 
ticulum ultimately  atrophies  and  disappears,  leaving  the  gland  en- 
tirely unconnected  with  the  surface.  The  gland  is  enclosed  in  a 
connective-tissue  capsule,  from  which  trabeculse  pass  into  the  organ 
forming  its  framework.  The  gland  cells  are  arranged  in  slightly 
convoluted  tubules  and  rest  upon  a  basement  membrane.  Between 
the  tubules  is  a  vascular  connective  tissue.  Some  of  the  gland  cells 
are  small  cuboidal  cells  with  nuclei  at  their  bases  and  a  finely  granular 
basophile  protoplasm  {chief  cells).  Others,  somewhat  less  numerous 
than  the  preceding,  are  larger  polygonal  cells  with  centrally  placed 
nuclei  and  protoplasm  containing  coarse  acidophile  (eosinophile)  gran- 
ules {chromophile  cells).  While  presenting  different  appearances  and 
usually  described  as  two  kinds  of  cells,  it  is  probable  that  chromophile 
cells  and  chief  cells  represent  merely  different  functional  conditions  of 
the  same  cell.  Some  alveoli  in  the  posterior  portion  of  the  lobe  fre- 
quently contain  a  colloid  substance  similar  to  that  found  in  the  thyroid. 

As  in  all  ductless  glands,  the  blood  supply  is  rich  and  the  rela- 
tions of  capillaries  to  gland  cells  are  extremely  intimate,  dense  net- 
works of  capillaries  surrounding  the  alveoli  on  all  sides. 

The  Posterior  Lobe. — This,  like  the  anterior,  is  surrounded  by 
a  connective-tissue  capsule  which  sends  trabeculse  into  its  substance. 
In  the  human  adult  the  lobe  consists  mainly  of  neuroglia  with  a 
few  scattered  cells,  which  probably  represent  rudimentary  ganglion 
cells.  In  the  human  embryo  and  in  many  adult  lower  animals, 
the  nervous  elements  are  much  more  prominent  and  more  definitely 
arranged.  Thus  Berkley  describes  the  posterior  lobe  of  the  pituitary 
body  of  the  dog  as  consisting  of  three  distinct  zones  :  (i)  An  outer 
zone  of  three  or  four  layers  of  cells  resembling  ependymal  cells. 
Connective-tissue  septa  from  the  capsule  separate  the  cells  into 
irregular  groups.  (2)  A  middle  zone  of  glandular  epithelium,  some 
of  the  cells  of  which  are  arranged  as  rather  indefinite  alveoli  which 


THE  NERVOUS  SYSTEM.  411 

may  contain  colloid.  (3)  An  inner  layer  of  nerve  cells  and  neuroglia 
cells.  These  react  to  the  Golgi  stain,  the  nerve  cells  having  axones  and 
dendrites.  Most  of  the  axones  appeared  to  pass  in  the  direction  of  the 
infundibulum,  but  could  not  be  traced  into  the  latter.  The  posterior 
lobe  is  of  ectodermic  origin,  developing  as  a  diverticulum  from  the 
floor  of  the  third  ventricle.  The  remains  of  the  diverticulum  consti- 
tute the  infundibulum. 

The  Pineal  Body. 

The  pineal  body  originates  as  a  fold  of  the  wall  of  the  primary 
brain  vescicle.  It  lies  at  first  upon  the  dorsal  surface  of  the  brain, 
and  in  some  lower  animals  continues  to  occupy  this  position.  Its 
ventral  position  in  the  higher  animals  and  in  man  is  due  to  the  great 
development  of  the  cerebral  hemispheres.  The  pineal  body  is  ap- 
parently of  the  nature  of  a  rudimentary  sense  organ,  being  some- 
times referred  to  as  the  median  or  pineal  eye.  In  man  it  is  sur- 
rounded by  a  firm  connective-tissue  capsule,  which  is  a  continuation 
of  the  pia  mater.  This  sends  trabecular  into  the  organ,  which  anas- 
tomose and  divide  it  into  many  small  chambers.  The  latter  contain 
tubules  or  alveoli  lined  with  cuboidal  epithelium.  This  may  be 
simple  or  stratified,  and  frequently  almost  completely  fills  the  tu- 
bules. Within  the  tubules  are  often  found  calcareous  deposits  known 
as  "  brain  sand." 

TECHNIC. 

The  general  structure  of  the  pituitary  body  and  of  the  pineal  body  can  be 
studied  by  fixing  material  in  formalin-M  filler's  fluid  (technic  5,  p.  5)  and  staining 
sections  with  haematoxylin-eosin  (technic  1,  p.  16). 

General  References  for  Further  Study. 

Barker :  The  Nervous  System  and  its  Constituent  Neurones,  New  York,  1899. 

Dejerine  :  Anatomie  des  centres  nerveux,  Paris,  1895. 

Van  Gehuchten:  Anatomie  du  systeme  nerveux  de  l'homme,  Louvaine,  1900. 

Golgi  :  Untersuchungen  fiber  den  feineren  Bau  des  centralen  und  peripheri- 
schen  Nervensystems,  Jena,  1894. 

Kolliker  :  Handbuch  der  Gewebelehre  des  Menschen.  Leipsic.  1896. 

Ramon  y  Cajal:  Beitrage  zum  Studieren  der  Medulla  Oblongata.  Leipsic. 
1896.— Les  nouvelles  idees  sur  la  structure  du  systeme  nerveux  chez  l'homme  et 
chez  les  vertebres.  Paris,  1894. 

Von  Lenhossek  :  Der  feinere  Bau  des  Nervensystems  im  Lichte  neuester  For- 
schungen.  Berlin,  1895. 

Obersteiner :  Anleitung  beim  Studieren  des  Baues  der  nervosen  Centralorgane, 
Leipsic,  1806. 

Marburg :  Atlas  des  menschlichen  Centralnervensystems,  Leipzig  und  Wien, 
1904. 


CHAPTER    XII. 

THE    ORGANS    OF    SPECIAL    SENSE. 

The  Organ  of  Vision. 

The  eyeball  and  optic  nerve  constitute  the  organ  of  vision.  To 
be  described  in  connection  with  them  are  the  eyelid  and  the  lacrymal 
apparatus. 

The  Eyeball  or  Bulbus  Oculi.— This  is  almost  spherical,  although 
slightly  flattened  antero-posteriorly.  It  consists  of  a  wall  enclosing 
a  cavity  filled  with  fluid. 

The  wall  of  the  eyeball  consists  of  three  coats  :  (a)  An  external 
fibrous  coat — the  sclera  and  cornea  ;  (p)  a  middle  vascular — the  cho- 
roid;  and  (c)  an.  internal  nervous — the  retina  (Fig.  265). 

The  Sclera  (Figs.  265  and  266). — This  consists  of  dense  fibrous 
tissue  with  some  elastic  fibres.  The  fibres  run  both  meridionally 
and  equatorially,  the  tendons  of  the  straight  muscles  of  the  eyeball 
being  continuous  with  the  meridional  fibres,  those  of  the  oblique 
muscles  with  the  equatorial  fibres.  The  few  cells  of  the  sclera  lie 
in  distinct,  very  irregular  cell  spaces,  and  frequently  contain  pigment 
granules.  Pigmented  cells  in  considerable  numbers  are  regularly 
present  near  the  corneal  junction,  at  the  entrance  of  the  optic  nerve, 
and  on  the  inner  surface  of  the  sclera.  Where  the  optic  nerve 
pierces  the  sclera,  the  continuity  of  the  latter  is  broken  by  the  enter- 
ing nerve  fibres,  forming  the  lamina  cribrosa  (Fig.  274).  The  pig- 
mented layer  of  the  sclera  next  the  choroid  is  known  as  the  lamina 
fusca,  and  is  lined  internally  by  a  single  layer  of  flat  non-pigmented 
endothelium.  Anteriorly  a  loose  connective  tissue  attaches  the 
sclera  to  the  scleral  conjunctiva. 

The  Cornea   (Figs.    267   and  270). — This   is   the  anterior  con- 
tinuation of   the   sclera  so  modified  as  readily  to  allow  the  light  to 
pass  through  it.       It  is  about  1  mm.  thick  and  consists  of  five  layers, 
which  from  before  backward  are  as  follows  (Fig.  267): 
(i)   Anterior  epithelium. 

412 


THE   ORGANS   OF  SPECIAL   SENSE. 


413 


(2)  Anterior  elastic  membrane  or  membrane  of  Bowman. 

(3)  Substantia  propria  corneae. 

(4)  Posterior  elastic  membrane  or  membrane  of  Descemet. 

(5)  Posterior  endothelium  or  endothelium  of  Descemet. 

(i)  The  anterior  epithelium  (Fig.  267,  /)  is  of  the  stratified 
squamous  type  and  consists  of  from  four  to  eight  layers  of  cells.  The 
deepest  cells  are  columnar  and  rest  upon  the  anterior  elastic  mem- 
brane.     The  middle  cells  are  polygonal  and  are  connected  by  short 


j  k 

Fig.  265.— Diagram  of  Eyeball  showing  Coats.  (Merkel-Henle.)  a,  Sclera  ;  b,  choroid  ;  c, 
retina  ;  d,  cornea  ;  e,  lens  ;  f,  iris  ;  £■,  conjunctiva  ;  //,  ciliary  body  ;  t,  sclero-corneal  junc- 
tion and  canal  of  Sehlemm  ;  J,  fovea  centralis  ;  k,  optic  nerve. 


intercellular  bridges.  The  surface  cells  are  flat.  Along  the  margin 
of  the  cornea  the  epithelium  is  continuous  with  that  of  the  conjunc- 
tiva (Fig.  270). 

(2)  The  anterior  clastic  membrane  (Fig.  267,  2)  is  a  highly 
developed  basement  membrane,  its  anterior  surface  being  pitted  to 
receive  the  bases  of  the  deepest  epithelial  cells.  It  is  apparently 
homogeneous,  and  while  called  an  elastic  membrane,  does   not   con- 


4H 


THE   ORGAXS. 


form   chemically  to   either  fibrous  or  elastic   tissue.      By  means   of 
special  technic,  a  fibrillar  structure  has  been  demonstrated. 

(3)  The  substantia  propria  (Fig.  267,  J)  constitutes  the  main 
bulk  of  the  cornea.  It  consists  of  connective  tissue  the  fibrils  of 
which  are  doubly  refracting  and  are  cemented  together  to  form  bun- 
dles and  lamellae.      In  the  human  cornea  the  lamellae  are  about  sixty 


Fig.  266.— Vertical  Section  through  Sclera,  Choroid,  and  Pigment  Layer  of  Retina.  (Merkel- 
Henle.)  A,  Sclera;  B,  choroid  ;  C,  pigmenr  layer  of  retina;  d,  lamina  suprachoroidea  ; 
e,  Haller's  layer  of  straight  vessels  ;  _/",  choriocapillaris  ;  j?,  vitreous  membrane 


in  number.  The  lamellae  are  parallel  to  one  another  and  to  the  sur- 
face of  the  cornea,  but  the  fibres  of  adjacent  lamellae  cross  one 
another  at  an  angle  of  about  twelve  degrees.  The  lamella?  are 
united  by  cement  substance.  Fibres  running  obliquely  through  the 
lamellae  from  posterior  to  anterior  elastic  membranes  hold  the  la- 
mellae firmly  together.  They  are  known  as  perforating  or  arcuate 
fibres. 

Between  the  lamellae  are  irregular  flat  cell  spaces  which  commu- 
nicate with  one  another  and  with  the  lymph  spaces  at  the  margin  of 
the  cornea  by  means  of  canal iculi.  Seen  in  sections  vertical  to 
the  surface  of  the  cornea,  these  spaces  appear  fusiform.  In  the 
spaces  are  the  connective-tissue  cells  of  the  cornea  or  cornea/  cor- 
puscles. These  are  flat  cells  corresponding  in  shape  to  the  spaces 
and  sending  out  processes  into  the  canaliculi  (Figs.  268  and  269). 

(4)  The  posterior  elastic  membrane  or  membrane  of  Dcsccmct 
(Fig.  267,  a\)  resembles  the  anterior,  but  is  much  thinner.  Like 
the  anterior,  it  does  not  give  the  chemical  reaction  of  elastic  tissue. 

(5)  The  posterior  endothelium  or  endothelium  of  Descemet  (Fig. 
2^7>  5)  consists  of  a  single  layer  of  flat  hexagonal  cells,  the  nuclei 
of  which  frequently  project  slightly  above  the  surface. 

The  cornea  contains  no  blood-vessels. 


THE   ORGANS   OF  SPECIAL   SENSE.  41 5 

The  Choroid. — This  is  made  up  of  four  layers  which  from  with- 
out inward  are  as  follows  (Fig.  266)  : 

(1)  The  lamina  suprachoroidea. 

(2)  The  layer  of  straight  vessels — Haller's  layer. 

(3)  The  capillary  layer — choriocapillaris. 

(4)  The  vitreous  membrane — lamina  citrea — membrane  of  Bruch. 

(1)  The  lamina  suprachoroidea  (Fig.  266,  d)  is  intimately  con- 
nected with  the  lamina  fusca  of  the  sclera  and  consists  of  loosely 
arranged  bundles  of  fibrous  and  elastic  tissue  among  which  are  scat- 
tered pigmented  and  non-pigmented  connective-tissue  cells.  Numer- 
ous lymph  spaces  are  found  between 
the  bundles  of  connective  tissue  and 
between  the  lamina  suprachoroidea  and 
lamina  fusca.  The  latter  are  known 
as  the  perichoroidal  lymph  spaces  (Fig. 
270). 

(2)  The  layer  of  straight  vessels 
(Fig.  266,  e)  consists  of  fibro-elastic 
tissue  containing  numerous  pigmented 
and  non  -  pigmented  cells,  support- 
ing the  large  blood-vessels  of  the 
layer.  The  latter  can  be  seen  with 
the  naked  eye,  and,  running  parallel 
straight  courses,  give  to  the  layer  a 
striated  appearance.  The  arteries  lie 
to  the  inner  side.  The  veins  which 
are  larger  than  the  arteries  converge 
toward  four  points — vencs  vorticoscc — 
one  in  each  quadrant  of  the  eyeball.  FlG.  z67. -vertical  Section  of  Cornea. 

A  narrow    boundary    ZOne,    rich     in  (Merkel-Henle.)   i,  Anterior  epithe- 

■*  Hum;  2,  anterior  elastic  membrane  : 

elastic  fibres   and  free  from  pigment,        3,  substantia  propria   corneas ;   4, 

,.       .  i-i  •     ,  n  t,    •  ,  posterior  elastic  membrane  ;  j.  pos- 

limits  this  layer  internally.     It  is  much        terior  endothelium. 

more  highly  developed  in  some  of  the 

lower  animals  than  in  man.      Formed  of  connective-tissue  bundles  in 

ruminants  and  horses,  it  is  known  as  the   tapetum  fibrosum,  while 

in  the  carnivora  its  structure — several  layers  of  flat  cells — gives  it 

the  name  of  the  tapetum  cellulosum. 

(3)  The    choriocapillaris   (Fig.    266,  /)    consists    of    connective 
tissue  supporting  a  dense  network  of  capillaries,  which  is  most  dense 


416 


THE   ORGANS. 


in  the  region  of  the  macula  lutea.  This  layer  is  usually  described  as 
free  from  pigment,  although  it  not  infrequently  contains  some  pig- 
mented cells. 

(4)  The  vitreous  membrane  (Fig.  266,  g)  is  a  clear,   apparently 


'M 


-    ■v^.'y.  JIP 


m 


:::-¥v-  ■■'     •■■■■•■  ■■■■.'.'..;'■     '•■;»•'■  ■/.{;>■'    .  .;•'•' '■■•■:■  ;-'-ir;r%i.;v;--;:f 

Fig.  268. — Section  of  Human  Cornea  cut   Tangential   to   Surface— X  350  (technic  y,  p.  71)— 
showing  corneal  cell  spaces  (lacunas)  and  anastomosing  canaliculi. 

structureless  membrane  about  two  microns  thick.  Its  outer  surface 
is  grooved  by  the  capillaries  of  the  choriocapillaris,  while  its  inner 
surface  is  pitted  by  the  retinal  epithelium. 


•"./' 


y  i'S<r y '  ■ 


A 

/'■'       '',;\.     ,'. 

$1           /  " 

V, 

'•...  y...„y.\ 

■y/ 

1 '"1.. 

1 

jft  .  1 1-  ■ 

, ./ 

;  f  ,..'■ 

. 

'•':'. 

1       \     \ 

"'T; 

• 

-■-''     .' 

.■.J"*- 

/         >     /    , 

--■■/. 

\       \ 

.'■'•■     s 

)          ■"    f      ' 

/                '"•■- 

1        

..-..A.  ,' 

PlG.   269,  —  Section  of   Human  Cornea  cut  Tangential   to    Surface — X   350  (technic  8,   p.   71)  — 
showing  corneal  cells  and  their  anastomosing  processes. 

The  CILIARY  Body.— This   is   the  anterior  extension  of  the  cho- 
roid and  consists  of  the  ciliary  processes  and  the  ciliary  muscle  (Fig. 


THE   ORGANS   OF  SPECIAL   SENSE. 


417 


270).  It  extends  from  the  ora  scrrata  (a  wavy  edge  which  marks  the 
anterior  limit  of  the  nervous  elements  of  the  retina — see  Retina)  to 
the  margin  of  the  iris  (see  below). 

The  ciliary  processes  (Fig.  270),  from  seventy  to  eighty  in  num- 
ber, are  meridionally-running  folds  of  the  choroid  from  which  are 
given  off  numerous  irregular  secondary  folds.  The  processes  begin 
low  at  the  ora  serrata,  gradually  increase  in  height  to  about  1  mm., 


iiilPL 
111  Will 

Cornea — BfilibpliF 


Anterior  chamber 


Canal  of  Schlemm 


Iris 

Pars  iridica  retinas 


Ciliary  process 


of  Fontana — sri  f  ■  •  Jr,-~  ■""■Vs^"-'7  '-'■'.   »|sfe   ~  Ji| Circular  fibres 

'  '        '  1  '■     ■  "Kf^^r^^S^    ii      °f  ciliary  muscle 

Conjunctiva"1 

"^Wi'ii        '"'-'' '  ■!  •  <•  (i^ rtaUial  fibres  of 

!       I !  1 1  HTOSSJsSttif  \ivi:s»  ■.:  1 : i  ciliary  muscle 


Par3  ciliaris  retinae 


Perichorioidal  lymph  space. 


FIG.  270. — Vertical  Section  through  Human  Sclero. corneal  Junction.     (Cunningham.) 


and  end  abruptly  at  the  margin  of  the  iris.  The  ciliary  processes 
consist  of  connective  tissue  containing  many  pigmented  cells  and 
supporting  numerous  blood-vessels.  Invaginations  lined  with  clear 
columnar  epithelium  have  been  described  as  ciliary  glands.  The 
ciliary  folds  are  covered  by  the  vitreous  membrane,  and  internal  to 
the  latter  is  a  continuation  forward  of  non-nervous  elements  of  the 
retina — pars  ciliaris  retime  (Fig.  270).  This  consists  of  two  layers 
of  columnar  epithelial  cells,  the  outer  layer  being  pigmented,  the 
inner  non-pigmented. 
27 


4i8 


THE   ORGANS. 


The  ciliary  muscle  (Fig.  270)  is  a  band  of  smooth  muscle  which 
encircles  the  iris.  It  lies  in  the  outer  anterior  part  of  the  ciliary 
body,  and  on  cross  section  has  a  generally  triangular  shape.  It  is 
divisible  into  three  groups  of  muscle  cells  :  (a)  An  inner  circular 
group  near  the  base  of  the  iris — circular  muscle  of  Miiller;  [/>)  an 
outer  meridional  group  lying  next  to  the  sclera  and  known  as  the 
tensor  choroideae,  and  (c)  a  middle  radial  group.  The  meridional 
and  radial  groups  both  take  origin  in  the  posterior  elastic  lamina  of 
the  cornea,  the  former  passing  backward  along  the  margin  of  the 
sclera  to  its  insertion  in  the  ciliary  body  near  the  ora  serrata,  the 
latter  radiating  fan-like  to  a  broad  insertion  in  the  ciliary  body  and 
processes. 

The  ciliary  body  is  closely  attached  to  the  sclero-corneal  junction 
by  the  ligamentum pectinatum  (Fig.  270),  a  continuation  of  the  pos- 
terior elastic  lamina  of  the  cornea.     Within  the  ligament  are  spaces 

(spaces  of  Fontanel)  lined  with  en- 
dothelium. These  are  apparently 
lymph  spaces,  and  communicate 
with  each  other,  with  similar  spaces 
around  the  canal  of  Schlemm,  and 
with  the  anterior  chamber.  The 
canal  of  Schlemm  (Fig.  270)  is  a 
venous  canal  which  encircles  the 
cornea,  lying  in  the  sclera  close  to 
the  corneal  margin.  Instead  of  a 
single  canal  there  may  be  several 
canals. 

The  Iris  (Fig.  271). — This  rep- 
resents  a   further  continuation  for- 
ward  of   the   choroid.      Its   base   is 
attached    to    the    ciliary    body  and 
ligamentum  pectinatum.     From  this 
point   it  extends   forward  as  a  dia- 
phragm   in    front    of    the    lens,   its 
centre  being  perforated  to  form  the 
pupillary  opening.      It   is  deeply  pigmented,  and  to  its   pigment  the 
color  of  the  eye   is  due.      Four  layers  may  be  distinguished,  which 
from  before  backward  are  as  follows 
(i  )   The  anterior  endothelium. 


ss^      b 


PIG.  271.  —Vertical  Section  through 
Iris.  (Merkel-Henle.)  a,  Anterior 
endothelium  ;  6,  stroma  or  substantia 
propria;  c,  vitreous  membrane;  d, 
pigment  layer  ;  v,  blood-vessel. 


THE  ORGANS   OF  SPECIAL  SENSE. 


419 


(2)  The  stroma. 

(3)  The  vitreous  membrane. 

(4)  The  pigmented  epithelium. 

(1)  The  anterior  endothelium  is  a  single  layer  of  pigmented  cells 
continuous  with  the  posterior  endothelium  of  the  cornea  (Fig.  271,  a). 

(2)  The  stroma  is  divisible  into  two  layers  :  an  anterior  reticular 
layer,  containing  many  cells,   some  of  which   are  pigmented,  and  a 

A  B 


Fig.  272. — A,  Scheme  of  retina  as  shown  by  the  Golgi  method.  />',  Vertical  section  of  retina  to 
show  layers  as  demonstrated  by  the  ha^matoxylin-eosin  stain.  (Merkel-Henle.)  B.—i, 
Layer  of  pigmented  epithelium  ;  2,  layer  of  rods  and  cones  ;  3,  outer  limiting  layer  ;  4, 
outer  nuclear  layer  ;  j,  outer  molecular  layer,  6,  inner  nuclear  layer  ;  7,  inner  molecular 
layer;  <?,  layer  of  nerve  cells;  g,  layer  of  nerve  fibres;  jo,  inner  limiting  layer.  A. — 
1,  Figment  layer  ;  2,  processes  of  pigmented  epithelial  cells  extending  down  between  rods 
and  cones;  3,  rods;  4,  red-ceil  nuclei  and  rod  fibres;  J,  cones;  6,  cone  fibres;  7,  bipolar 
cells  of  inner  nuclear  layer  ;  <?,  ganglion  cells  of  nerve-cell  layer  ;  9,  larger  ganglion  cells 
of  nerve-cell  layer  ;  jo,  fibres  of  optic  nerve  forming  layer  of  nerve  fibres  ;  //  and  12,  types 
of  horizontal  cells;  73,  74,  73,  and  /6,  types  of  cells  the  bodies  of  which  lie  in  the  inner 
nuclear  layer;  /-,  efferent  optic-nerve  fibre  ending  around  cell  of  inner  nuclear  layer; 
/<?,  neuroglia  cells  ;  79,  Muller's  fibre  ;  20,  rod-bipolar  cell  of  inner  nuclear  layer. 

vascular  layer,  the  vessels  of  which  are  peculiar  in  that  their  walls 
contain  almost  no  muscle,  but  have  thick  connective-tissue  sheaths. 
In  the  posterior  part  of  the  stroma  are  bundles  of  smooth  muscle. 
Those  nearest  the  pupillary  margin  encircle  the  pupil  forming  its 
sphincter  muscle,  while  external  are  scattered  radiating  bundles 
forming  the  dilator  muscle. 


42  o  THE   ORGANS. 

(3)  The  vitreous  membrane  is  continuous  with,  and  has  the  same 
structure  as  the  membrane  of  Bruch. 

(4)  The  pigmented  epithelium  (Fig.  271,  d)  consists  of  several 
layers  of  cells  and  is  continuous  with  the  pars  ciliaris  retinae.  Ex- 
cept in  albinos,  both  layers  are  pigmented. 

The  Retina. — The  retina  is  the  nervous  tunic  of  the  eye.  It 
lines  the  entire  eyeball,  ending  only  at  the  pupillary  margin  of  the 
iris.  Its  nervous  elements,  however,  extend  only  to  the  ora  serrata, 
which  marks  the  outer  limit  of  the  ciliary  body  (Fig.  270).  The 
nervous  part  of  the  retina  is  known  as  the  pars  optica  retince,  the 
non-nervous  extension  over  the  ciliary  processes  as  the  pars  ciliaris 
retime,  its  further  continuation  over  the  iris  as  the  pars  iridica  retince. 
Modifications  of  the  optic  portion  of  the  retina  are  found  in  the 
region  of  the  macula  lutea  and  of  the  optic  nerve  entrance. 

The  Pars  Optica  Retime. — This  is  the  only  part  of  the  retina 
directly  concerned  in  the  reception  of  impulses,  and  may  be  re- 
garded as  the  extremely  complex  sensory  end-organ  of  the  optic 
nerve.  It  is  divisible  into  ten  layers,  which  from  without  inward 
are  as  follows  (Fig.  272) : 

(1 )  Layer  of  pigmented  epithelium. 

(2)  Layer  of  rods  and  cones. 

(3)  Outer  limiting  membrane.  \  Layer  of  neuro-epithelium. 

(4)  Outer  nuclear  layer. 
(51    Outer  molecular  layer. 
(6)  Inner  nuclear  layer. 
Cj)   Inner  molecular  layer. 

(8)  Layer  of  nerve  cells. 

(9)  Layer  of  nerve  fibres. 
(10)   Inner  limiting  membrane. 
The  layer  of  pigmented  epithelium  (Fig.  272,  B,  /)  consists  of  a 

single  layer  of  regular  hexagonal  cells  (Fig.  20,  p.  59).  The 
nuclei  lie  in  the  outer  part  of  the  cell,  while  from  the  inner  side 
thread-like  projections  extend  down  between  the  rods  and  cones  of 
the  layer  next  internal.  The  pigment  has  the  form  of  rod-shaped 
granules.  Its  distribution  seems  to  depend  upon  the  amount  of 
light  being  admitted  to  the  retina.  When  little  or  no  light  is  being 
admitted,  the  pigment  is  found  in  the  body  of  the  cell,  the  processes 
being  wholly  or  almost  free  from  pigment;  when  the  retina  is  ex- 
posed  to  a  bright  light,  some  of  the  pigment  granules   pass  down 


Ganglionic  layer. 


THE  ORGANS   OF  SPECIAL   SENSE.  421 

into  the  processes  so  that  the  pigment  becomes  more  evenly  distrib- 
uted throughout  the  cell. 

The  layer  of  rods  and  cones  and  the  outer  nuclear  layer  (Fig. 
272,  B,  2,  4)  are  best  considered  as  subdivisions  of  a  single  layer, 
the  neuro-epithelial  layer.  This  consists  essentially  of  two  forms 
of  neuro-epithelial  elements,  rod  visual  cells  and  cone  visual  cells. 
These,  with  supporting  connective  tissue,  constitute  the  layer  of 
rods  and  cones  and  the  outer  nuclear  layer,  the  separation  into  sub- 
layers being  due  to  the  sharp  demarcation  between  the  nucleated 
and  non-nucleated  parts  of  the  cells  and  the  separation  of  the  two 
parts  by  the  perforated  outer  limiting  membrane. 

The  rod  visual  cell  (Fig.  272,  A,  4)  consists  of  rod,  rod-fibre, 
and  nucleus.  The  rod  (Fig.  272,  A,  j)  is  a  cylinder  from  30  to  40  ;j. 
in  length  and  about  2  //  in  diameter.  It  is  divisible  into  an  outer 
clear  portion,  which  contains  the  so-called  "visual  purple"  and  an 
inner  granular  portion.  At  the  outer  end  of  the  latter  is  a  fibrillated 
ellipsoidal  body,  much  more  distinct  in  some  of  the  lower  animals, 
the  ellipsoid  of  Krause.  At  its  inner  end  the  rod  tapers  down  to  a 
fine  fibre,  the  rod  fibre,  which  passes  through  a  perforation  in  the 
outer  limiting  membrane  into  the  outer  nuclear  layer,  where  it  ex- 
pands and  contains  the  nucleus  of  the  rod  visual  cell.  These  nuclei 
are  situated  at  various  levels  in  the  fibre  and  constitute  the  most 
conspicuous  element  of  the  outer  nuclear  layer  (Fig.  272,  B,  f). 

The  cone  visual  cell  (Fig.  272,  A,  j,  6)  consists  of  cone,  cone- 
fibre,  and  nucleus.  The  cone  (Fig.  272,  A,  5)  is  shorter  and  broader 
than  the  rod,  and  like  the  latter  is  divisible  into  two  parts.  The  outer 
part  is  short,  clear,  and  tapering,  the  inner  part  broad  and  granular, 
and  like  the  rod  contains  a  fibrillated  ellipsoid  body.  The  cone  fibre 
(Fig.  272,  A,  6)  is  much  broader  than  the  rod  fibre,  passes  completely 
through  the  outer  nuclear  layer  and  ends  in  an  expansion  at  the  mar- 
gin of  the  outer  molecular  layer.  The  nucleus  of  the  cone  cell  usu- 
ally lies  just  beneath  the  outer  limiting  membrane. 

The  remaining  layers  of  the  retina  must  be  considered  in  relation 
on  the  one  hand  to  the  neuro-epithelium,  on  the  other  to  the  optic 
nerve.  The  inner  nuclear  layer  (Fig.  272,  B,  6)  and  the  layer  of 
nerve  cells  (Fig.  272,  B,  8)  are  composed  largely  of  nerve-cell  bodies, 
while  the  two  molecular  layers  (Fig.  272,  B,  5,  7)  are  formed  mainly 
of  the  ramifications  of  the  processes  of  these  cells.  In  the  inner 
nuclear  layer  are  two  kinds  of  nerve  elements,  rod  bipolar  cells  and 


422  THE   ORGANS. 

cone  bipolar  cells.  The  bodies  of  these  cells  with  their  large  nuclei 
form  the  bulk  of  this  layer.  From  the  rod  bipolars  (Fig.  272,  A,  20) 
processes  {dendrites)  pass  outward  to  ramify  in  the  outer  molecular 
layer  around  the  terminations  of  the  rod  fibres.  From  the  cone  bi- 
polars (Fig.  272,  A,  7)  similar  processes  (dendrites)  extend  into  the 
outer  molecular  layer  where  they  ramify  around  the  termination  of 
the  cone  cells.  Two  other  forms  of  nerve  cells  occur  in  the  inner 
nuclear  layer.  One  is  known  as  the  horizontal  cell  (Fig.  272,  A,  12). 
Its  processes  ramify  almost  wholly  in  the  outer  molecular  layer.  The 
other  lies  along  the  inner  margin  of  the  inner  nuclear  layer  and 
sends  its  dendrites  into  the  inner  molecular  layer  (Fig.  272,  A,  ij, 
i/j.,  ly,  and  16).  Many  of  these  latter  cells  appear  to  have  no  axone 
and  are  consequently  known  as  amacrine  cells. 

The  outer  molecular  layer  is  thus  seen  to  be  formed  mainly  of 
terminations  of  the  rod  and  cone  visual  cells,  of  the  dendrites  of  the 
rod  and  cone  bipolars,  and  of  the  processes  of  the  horizontal  cells. 

From  the  cone  bipolar  a  process  {axone)  extends  inward  to 
ramify  in  the  inner  molecular  layer,  while  from  the  rod  bipolar  a 
process  (axone)  passes  inward  through  the  inner  molecular  layer  to 
terminate  around  the  cells  of  the  nerve-cell  layer. 

The  layer  of  nerve  cells  (Fig.  272,  B,  8)  consists  for  the  most 
part  of  large  ganglion  cells  whose  dendrites  ramify  in  the  inner  mo- 
lecular layer,  and  whose  axones  pass  into  the  layer  of  nerve  fibres 
and  thence  into  the  optic  nerve.  Some  small  ganglion  cells  are  also 
found  in  this  layer,  especially  in  the  region  of  the  macula  lutea 
(see  page  423). 

The  inner  molecular  layer  is  thus  seen  to  be  composed  mainly 
of  the  processes  (axones)  of  the  rod  and  cone  bipolars  and  of  the 
dendrites  of  the  ganglion  cells  of  the  nerve-cell  layer. 

The  layer  of  nerve  fibres  (Fig.  272,  B,  p)  consists  mainly  of  the 
axones  of  the  just-described  ganglion  cells,  although  a  few  centrifu- 
gal axones  of  brain  cells  (Fig.  272,  A,  ij)  are  probably  intermingled. 

The  outer  and  inner  limiting  layers  or  membranes  (Fig.  272,  />', 
j,  10)  are  parts  of  the  sustentacular  apparatus  of  the  retina,  being 
connected  with  the  cells  or  fibres  of  Miillcr  (Fig.  272,  A,  /p  and 
Fig.  273).  The  latter  form  the  most  conspicuous  elements  of  the 
supportive  tissue  of  the  retina.  They  are  like  the  nerve  elements 
proper,  of  ectodermic  origin  and  are  elongated  cells  which  extend 
through  all  the  retinal  layers,  excepting  the  layer  of  rods  and  cones 


THE   ORGANS   OF  SPECIAL   SENSE. 


42  3 


and  the  pigment  layer.  The  inner  ends  of  the  cells,  which  are  coni- 
cal and  fibrillated,  unite  to  form  the  inner  limiting  membrane  (Fig. 
273,  10).  Through  the  inner  molecular  layer  the  cell  takes  the  form 
of  a  narrow  stalk  with  numerous  fringe-like  side  fibrils  (Fig.  273,  7). 
This  widens  in  the  inner  nuclear  layer,  where  cup-like  depressions  in 
the  sides  of  the  Midler's  cell  are  caused  by  the  pressure  of  the  sur- 
rounding nerve  cells  (Fig.  273,  b).  This 
wide  portion  of  the  cell  in  the  inner  nuclear 
layer  contains  the  nucleus  (Fig.  273,  a). 
In  the  outer  molecular  layer  the  cell  again 
becomes  narrow  (Fig.  273,  5)  and  in  the 
outer  nuclear  layer  broadens  out  into  a 
sponge-like  reticulum  (Fig.  273,  f),  which 
supports  the  rod  and  cone  bipolars.  At 
the  inner  margin  of  the  layer  of  rods  and 
cones  the  protoplasm  of  the  Midler's  cells 
spreads  out  and  unites  to  form  the  so- 
called  outer  limiting  membrane  (Fig.  273, 
j),  from  which  delicate  fibrils  {fibre  baskets) 
pass  outward  between  the  rods  and  cones. 
In  addition  to  the  Midler's  cells,  which  are 
neuroglia  elements,  spider  cells  also  occur 
in  the  retina  (Fig.  272,  A,  18). 

The  retina  of  the  macula  lutea  presents 
certain  peculiarities.  Its  name  is  derived 
from  the  yellow  pigment  which  is  distrib- 
uted diffusely  through  the  inner  layers,  ex- 
tending as  far  out  as  the  outer  molecular 
layer.  The  ganglion-cell  layer  and  the 
inner  nuclear  layer  are  thicker  than  in  other 
parts  of  the  retina.  In  the  layer  of  rods 
and  cones  there  is  a  gradual  reduction  in 
the  number  of  rods,  while  the  number  of 
cones  is  correspondingly  increased. 

In  the  centre  of  the  macula  is  a  depression,  the  fovea  centralis. 
As  the  retina  approaches  this  area  it  becomes  greatly  thinned,  little 
remaining  but  the  layer  of  cone  cells  and  the  somewhat  thickened 
layer  of  pigmented  epithelium. 

At  the  ora  serrata  the  nervous  elements  of  the  retina  cease.     The 


Fig.  273. -Two  Muller's  Fibres 
from  Retina  of  Ox  showing 
Relation  to  Layers  of  Retina. 
(Ramon  y  Cajal.)  _?,  Outer 
limiting  layer  ;  4,  outer  nu- 
clear layer  \s,  outer  molecular 
layer;  6,  inner  nuclear  layer; 
7,  inner  molecular  layer  ;  S, 
layer  of  nerve  cells  ;  q,  layer  of 
nerve  fibres  ;  10,  inner  limiting 
layer;  a,  nucleus;  b,  cup-like 
depression  caused  by  pressure 
from  surrounding  cells. 


424 


THE   ORGANS. 


non-nervous  retinal  extension  over  the  ciliary  body  {pars  ciliaris  re- 
time) and  over  the  iris  {pars  iridica  retince)  have  been  described  in 
connection  with  the  ciliary  body  and  iris. 

The  Optic  Nerve. — The  optic  nerve  (Fig.  274,  d)  is  enclosed 
by  two   connective-tissue  sheaths,  both  of  which  are   extensions   of 

the  brain  membranes.  The 
outer  dural  sheath  (Fig.  274, 

a)  is  continuous  with  the 
dura  mater  of  the  brain  pos- 
teriorly, while  anteriorly  it 
blends  with  the  sclera.  The 
inner  pial  sheath  (Fig.  274, 

b)  is  an  extension  of  the  pia 
mater  and  is  separated  from 
the  outer  sheath  by  the  sub- 
dural space  (Fig.  274,  c). 
The  pial  sheath  is  divisible 
into  two  sub- layers :  an 
outer  fibrous  layer  (the  so- 
called  arachnoid),  and  an 
inner  vascular  layer.  These 
two  layers  are  separated  by 
a  narrow  space,  the  subar- 
achnoid space.  The  optic 
nerve  fibres,  in  passing 
through  the  sclera  and  cho- 
roid, separate  the  connec- 
tive-tissue bundles  so  that 
they  form  a  lattice-work,  the 
already    mentioned    lamina 

cribrosa  (Fig.  274,  //).  The  optic  nerve  fibres  are  medullated,  but 
have  no  neurilemma.  As  they  pass  through  the  lamina  cribrosa 
the  medullary  sheaths  are  lost,  the  fibres  reaching  the  retina  as  naked 
axones. 

Relations  of  Optic  Nerve  to  Retina  and   Brain. 

The  rod  and  cone  visual  cells  are  the  neuro-epithelial  beginnings 
of  the  visual  tract  (Fig.  272,  A,  J,  ./,  5,  and  6).  By  their  expanded 
bases  in  the  outer   molecular  layer,  the  rod  and  cone  cells  commu- 


FlO.  274.— Section  through  Entrance  of  Optic  Nerve 
into  Eyeball.  CMerkel-Henle.)  a,  Dural  sheath; 
b,  pial  sheath,  inner  and  outer  layers;  c,  space  be- 
tween inner  and  outer  layers  of  pia  mater  ;  d, 
optic  nerve  ;  <?,  central  artery  of  retina  ;  u',  sclera  ; 
/,  choroid  ;  g;  retina  ;  //,  lamina  cribrosa. 


THE   ORGANS    OF  SPECIAL   SENSE. 


4^5 


nicate  with  the  neurone  system  No.  I.  of  the  optic  tract.  This 
comprises  (^)  rod  neurones,  (b)  cone  neurones,  (e)  horizontal  neu- 
rones. 

Neurone  System  No.  I. — (a)  Rod  neurones.  The  cell  bodies 
of  these  neurones  (Fig.  272,  A,  20)  lie  in  the  inner  nuclear  layer. 
Their  dendrites  enter  the  outer  molecular  layer  where  they  form  net- 
works around  the  expanded  bases  of  the  rod  cells.  Their  axones 
pass  through  the  inner  molecular  layer  and  end  in  arborizations 
around  the  bodies  and  dendrites  of  cells  of  the  nerve  cell  layer  (neu- 
rone system  No.  II.).  (b)  Cone 
neurones  (Fig.  272,  A,  7).  These 
have  their  cell  bodies  in  the  inner 
nuclear  layer.  Their  dendrites 
pass  to  the  outer  molecular  layer 
where  they  form  networks  around 
the  expanded  bases  of  the  cone 
cells.  Their  axones  pass  only 
into  the  inner  molecular  layer  7V 
where  they  end  in  arborizations 
around  the  dendrites  of  neurones 
whose  cell  bodies  are  in  the 
layer  of  nerve  cells  (neurone  sys- 
tem No.  II.).  (c)  Horizontal 
neurones  (Fig.  272,  A,  II  and 
12.  These  serve  as  association 
neurones  between  the  visual  cells 
and  may  be  divided  into  rod 
association  neurones  and  cone  as- 
sociation neurones.  The  cone 
association  neurones  are  the 
smaller  and  more  superficial,  and 
both  dendrites  and  axones  end  in 
the  outer  molecular  layer  around 
the  terminal  expansions  of  the 
cone  visual  cells  (Fig.  272,  A, 
II).  The  rod  association  neu- 
rones are  larger,  more  deeply  seated,  and  behave  in  a  similar  man- 
ner toward  the  rod  visual  cells  (Fig.  272,  A,  12).  Some  of  these 
cells  send  processes  to  the  inner  molecular  layer. 


Fig.  275. — Diagram  showing  Main  Relations 
of  Optic  Tract.  (Testut.)  R,  Retina  ;  No, 
optic  nerve  ;  CM,  optic  decussation  or  chi- 
asma  ;  Tro,  optic  tract  ;  Tho,  thalamus  ; 
Cgl,  lateral  geniculate  body  ;  Qa,  anterior 
corpus  quadrigeminum  ;  Rd,  fibre  of  optic 
tract  passing  directly  to  cortex  ;  S>//,  third 
neurone  system  of  optic  tract  (excepting 
Rd)  connecting  thalamus,  lateral  genicu- 
late body,  and  anterior  corpus  quadrigem- 
inum with  the  cortex,  Co. 


426  THE   ORGANS. 

Neurone  System  No.  II. — This  has  been  already  partly  de- 
scribed in  connection  with  the  axone  terminations  of  neurone  system 
No.  I.  The  cell  bodies  of  the  second  neurone  system  (Fig.  272,  A, 
S,  p)  are  in  the  layer  of  nerve  cells  and  are,  as  above  noted,  associ- 
ated either  directly  or  by  means  of  their  dendrites  with  the  axones 
of  the  first  neurone  system.  Their  axones  pass  into  the  layer  of 
nerve  fibres  and  ultimately  become  fibres  of  the  optic  nerve  (Fig. 
272,  A,  10). 

The  optic  nerves  (Fig.  275,  No)  unite  at  the  base  of  the  brain  to 
form  the  optic  decussation  or  chiasma  (Fig.  275,  CM).  Here  the 
axones  from  the  mesial  part  of  the  retina  cross  to  the  optic  tract  of 
the  opposite  side,  while  those  of  the  lateral  part  of  the  retina  remain 
in  the  optic  tract  of  the  same  side.  The  axones  of  the  optic  tract 
(Fig.  275,  Tro)  terminate  in  the  thalamus,  in  the  lateral  geniculate 
body,  and  in  the  anterior  corpus  quadrigeminum  (Fig.  275). 

Neurone  System  No.  III. — The  neurones  of  this  system  have 
their  cell  bodies  in  the  thalamus,  lateral  geniculate  body,  and  ante- 
rior corpus  quadrigeminum  (Fig.  275).  Their  axones  terminate  in 
the  cortical  visual  centres  in  the  occipital  lobe  (Fig.  275,  Co). 
Some  few  axones  of  retinal  neurones  may  pass  the  above  nuclei  to 
terminate  directly  in  the  cortex  (Fig.  275,  Rd). 

The  Lens. — The  lens  is  composed  of  lens  fibres  which  are  laid 
down  in  layers  (Fig.  276,  a).  The  lens  fibre  is  a  long  hexagonal, 
flattened  prism  with  serrated  edges.  Most  of  the  lens  fibres  are 
nucleated,  the  nucleus  lying  at  about  the  centre  of  the  fibre  near  the 
axis  of  the  lens.  The  most  central  of  the  lens  fibres  are  usually 
non-nucleated.  The  fibres  extend  meridionally  from  before  back- 
ward through  the  entire  thickness  of  the  lens.  They  are  united  by 
a  small  amount  of  cement  substance.  The  lens  is  surrounded  by 
the  lens  capsule  (Fig.  276,  /;),  a  clear  homogeneous  membrane  which 
is  about  12  //.  thick  over  the  anterior  surface  of  the  lens,  about  half 
as  thick  over  the  posterior  surface.  Between  the  capsule  and  the 
anterior  and  lateral  surfaces  of  the  lens  is  a  single  layer  of  cuboidal 
epithelial  cells  (Fig.  276,  c),  the  lens  epithelium.  Attached  to  the 
capsule  of  the  lens  anteriorly  and  posteriorly  are  membrane-like 
structures  which  constitute  the  suspensory  ligament  of  the  lens. 
These  pass  outward  and  unite  to  form  a  delicate  membrane,  the 
zonula  ciliaris  or  zonule  of  Zinn  (Fig,  270).     This  bridges  over  the 


THE   ORGANS   OF  SPECIAL   SENSE. 


427 


inequalities  of  the  ciliary  processes  and,  continuing  as  the  hyaloid 
membrane,  forms  a  lining  for  the  vitreous  cavity  of  the  eye.  The 
triangular  space  between  the  two  layers  of  the  suspensory  ligament 
and  the  lens  is  known  as  the  canal  of  Petit. 

The  vitreous  body  is,  a  semifluid  substance  containing  fibres  which 
run  in  all  directions  and  a  small   number  of  connective-tissue  cells 
and  leucocytes.      Traversing  the  vitreous  in  an  antero-posterior  direc- 
tion   is    the     so-called     hyaloid    or 

h     r  a  ~ 

Cloquef  s  canal,  the  remains  of  the 
embryonic  hyaloid  artery  (page 
428). 

Blood-vessels.  —  The    blood-ves- 
sels   of    the    eyeball    are    divisible 


Fig.  276.  Fig.  277. 

Fig.  276.-From  Longitudinal  Section  through  Margin  of  Crystalline  Lens,  showing  longitud- 
inal sections  of  lens  fibres  and  transition  from  epithelium  of  capsule  into  lens  fibres. 
(Merkel-Henle.)     a,  Lens  fibres;  b,  capsule;  c,  epithelium. 

Fig.  277. — From  Cross  Section  of  Crystalline  Lens,  showing  transverse  sections  of  lens  fibres 
and  surface  epithelium.     (Merkel-Henle.)     a,  Lens  fibres  ;  fr,  epithelium. 


into  two  groups,  one  group  being  branches   of  the  central  artery  of 
the  retina,  the  other  being  branches  of  the  ciliary  artery. 

The  central  artery  of  the  retina  enters  the  eyeball  through  the 
centre  of  the  optic  nerve.  Within  the  eyeball  it  divides  into  two 
branches,  a  superior  and  an  inferior.  These  pass  anteriorly  in  the 
nerve-fibre  layer,  giving  off  branches,  which  in  turn  give  rise  to  cap- 
illaries which  supply  the  retina,  passing  outward  as  far  as  the  neuro- 
epithelial layer  and  anteriorly  as  far  as  the  ora  serrata.      The  smaller 


42  S  THE  ORGANS. 

branches  of  the  retinal  arteries  do  not  anastomose.  In  the  embryo  a 
third  vessel  exists,  the  hyaloid  artery.  This  is  a  branch  of  the  cen- 
tral retinal  artery  and  traverses  the  vitreous  to  the  posterior  surface 
of  the  lens,  supplying  these  structures.  The  hyaloid  canal,  or  canal 
of  Cloquet,  of  the  adult  vitreous,  represents  the  remains  of  the  degen- 
erate hyaloid  artery  (page  427).  The  veins  of  the  retina  accompany 
the  arteries. 

The  ciliary  arteries  are  divisible  into  long  ciliary  arteries,  short 
ciliary  arteries,  and  anterior  ciliary  arteries.  The  long  ciliary  arte- 
ries are  two  in  number  and  pass  one  on  each  side  between  the  cho- 
roid and  sclera  to  the  ciliary  body,  where  each  divides  into  two 
branches,  which  diverge  and  run  along  the  ciliary  margin  of  the  iris. 
Here  the  anastomosis  of  the  two  long  ciliary  arteries  forms  the 
greater  arterial  circle  of  the  iris.  This  gives  rise  to  small  branches 
which  pass  inward  supplying  the  surrounding  tissues  and  unite  near 
the  margin  of  the  pupil  to  form  the  lesser  arterial  circle  of  the  iris. 
The  branches  of  the  short  ciliary  arteries  pierce  the  sclera  near  the 
optic  nerve  entrance,  supply  the  posterior  part  of  the  sclera,  and  ter- 
minate in  the  choriocapillaris  of  the  choroid.  The  anterior  ciliary 
arteries  enter  the  sclera  near  the  corneal  margin  and  communicate 
with  the  choriocapillaris  and  with  the  greater  arterial  circle  of  the 
iris.  The  anterior  ciliary  arteries  also  supply  the  ciliary  and  recti 
muscles  and  partly  supply  the  sclera  and  conjunctiva.  Small  veins 
accompany  the  ciliary  arteries;  the  larger  veins  of  this  area  are 
peculiar,  however,  in  that  they  do  not  accompany  the  arteries,  but 
as  venae  vorticosae  converge  toward  four  centres,  one  in  each  quad- 
rant of  the  eyeball.  At  the  sclero-corneal  junction  is  a  venous 
channel,  the  canal  of  Schlemm,  which  completely  encircles  the  cornea 
(Fig.  270). 

Lymphatics. — The  eyeball  has  no  distinct  lymph-vessel  system. 
The  lymph,  however,  follows  certain  definite  directions  which  have 
been  designated  by  Schwalbe  "lymph  paths."  He  divides  them 
into  anterior  lymph  paths  and  posterior  lymph  paths.  The  anterior 
lymph  paths  comprise  (a)  the  anterior  chamber  which  communicates 
by  means  of  a  narrow  cleft  between  iris  and  lens  with  the  posterior 
chamber;  (p)  the  posterior  chamber;  (c)  the  lymph  canaliculi  of  the 
sclera  and  cornea  and  the  canal  of  Petit.  The  posterior  lymph  paths 
include  (a)  the  hyaloid  canal  (see  above)  ;  (/>)  the  subdural  and  in- 
trapial   spaces,  including  the  capsule  of  Tenon;   (c)  the  perichoroidal 


THE   ORGANS   OF  SPECIAL   SENSE.  429 

space,  and  id)  the  perivascular  and  pericellular  lymph  spaces  of  the 
retina. 

Nerves. — The  nerves  which  supply  the  eyeball  pass  through  the 
sclera  with  the  optic  nerve  and  around  the  eyeball  in  the  supracho- 
roid layer.     From  these  nerves,  branches  are  given  off  as  follows : 

(1)  To  the  choroid,  where  they  are  intermingled  with  ganglion 
cells. 

(2)  To  the  ciliary  body,  where  they  are  mingled  with  ganglion 
cells  to  form  the  ciliary  plexus.  The  latter  gives  off  branches  to  the 
ciliary  body  itself,  to  the  iris,  and  to  the  cornea.  Those  to  the  cor- 
nea first  form  a  plexus  in  the  sclera — the  plexus  annularis — which 
encircles  the  cornea.  From  this,  branches  pierce  the  substantia  pro- 
pria of  the  cornea,  where  they  form  four  corneal  plexuses,  one  in  the 
posterior  part  of  the  substantia  propria,  a  second  just  beneath  the 
anterior  elastic  membrane,  a  third  sub-epithelial,  and  a  fourth  intra- 
epithelial. The  fibres  of  the  last  named  are  extremely  delicate  and 
terminate  freely  between  the  epithelial  cells.  Krause  describes  end- 
bulbs  as  occurring  in  the  substantia  propria  near  the  margin  of  the 
sclera,  while  according  to  Dogiel  some  of  the  fibres  are  connected 
with  end-plates. 

The  Lacrymal  Apparatus. 

The  lacrymal  apparatus  of  each  eye  consists  of  the  gland,  its  ex- 
cretory ducts,  the  lacrymal  canal,  the  lacrymal  sac,  and  the  nasal 
duct. 

The  lacrymal  gland 'is  a  compound  tubular  gland  consisting  of 
two  main  lobes.  Its  structure  corresponds  in  general  to  that  of  a 
serous  gland.  The  excretory  ducts  are  lined  with  a  two-layered  col- 
umnar epithelium  which  becomes  simple  columnar  in  the  smaller 
ducts.  The  alveoli  are  lined  with  irregularly  cuboidal  serous  cells, 
which  rest  upon  a  basement  membrane  beneath  which  is  a  richly 
elastic  interstitial  tissue. 

The  lacrymal  canals  have  a  stratified  squamous  epithelial  lining. 
This  rests  upon  a  basement  membrane  beneath  which  is  the  stroma 
containing  many  elastic  fibres.  External  to  the  connective  tissue 
are  some  longitudinal  muscle  fibres. 

The  lacrymal  sac  is  lined  with  a  two-layered  stratified  or  pseudo- 
stratified  columnar  epithelium  resting  upon  a  basement  membrane. 
The  stroma  contains  much  diffuse  lymphatic  tissue. 


430  THE   ORGANS. 

The  nasal  duct  has  walls  similar  in  structure  to  those  of  the  lac- 
rymal  sac.  In  the  case  of  both  sac  and  duct  the  walls  abut  against 
periosteum,  a  dense  vascular  plexus  being  interposed. 

The  blood-vessels,  lymphatics,  and  nerves  of  the  lacrymal  gland 
have  a  distribution  similar  to  those  of  other  serous  Hands. 


The  Eyelid. 

The  eyelid  consists  of  an  outer  skin  layer,  an  inner  conjunctival 
layer,  and  a  middle  connective  tissue  layer. 

The  epidermis  is  thin  and  the  papillae  of  the  derma  are  low. 
Small  sebaceous  glands,  sweat  glands,  and  fine  hairs  are  present. 

The  conjunctiva  (Fig.  278,  a7)  is  a  mucous  membrane  consisting 
of  a  lining  epithelium  and  a  stroma.  The  epithelium  is  stratified 
columnar  consisting  of  two  or  three  layers  of  cells.  Among  these 
cells  are  cells  resembling  goblet  cells.  Although  not  always  upon 
the  surface,  they  are  believed  to  be  mucous  cells,  probably  analogous 
to  the  so-called  Leydig's  cells  found  in  the  larvae  of  amphibians  and 
fishes.  Diffuse  lymphoid  tissue  is  regularly  present  in  the  stroma, 
while  lymph  nodules  are  of  rare  occurrence.  Small  glands,  similar 
to  the  lacrymal  glands  in  structure,  are  usually  present  (Fig.  278,  /'). 

At  the  margin  of  the  eyelid  where  skin  joins  mucous  membrane 
are  several  rows  of  large  hairs,  the  eyelashes  (Fig.  278,  h).  Con- 
nected with  their  follicles  are  the  usual  sebaceous  glands  (Fig.  27S, 
g)  and  the  glands  of  Mall,  the  latter  probably  representing  modified 
sweat  glands. 

The  middle  layer  contains  the  tarsus  (Fig.  278,  e)  and  the  mus- 
cular structure  of  the  eyelid  (Fig.  278,  /;).  The  tarsus  is  a  plate  of 
dense  fibrous  tissue  which  lies  just  beneath  the  conjunctiva  and  ex- 
tends about  two-thirds  the  height  of  the  lid.  It  contains  the  tarsal 
or  Meibomian  glands  (Fig.  278,  c).  These  are  from  thirty  to  forty 
in  number,  each  consisting  of  a  long  duct  which  opens  externally  on 
the  margin  of  the  lid  behind  the  lashes  (Fig.  278,  f),  and  internally 
into  a  number  of  branched  tubules.  The  duct  is  lined  with  stratified 
squamous  epithelium.  The  tubules  resemble  those  of  the  sebaceous 
glands.  Between  the  tarsus  and  the  skin  are  the  muscular  structures 
of  the  eyelid  in  which  both  smooth  and  striated  muscle  are  found. 

Blood-vessels. — Two  main  arteries  pass  to  the  eyelid,  one  at  each 
angle  and  unite  to  form  an  arch,  the  tarsal  arch,  along  the  margin  of 


THE   ORGANS   OF  SPECIAL   SENSE. 


431 


the  lid.  A  second  arch,  the  external  tarsal  arch,  is  formed  along  the 
upper  margin  of  the  tarsus.  From  these  arches  are  given  off  capil- 
lary networks  which  supply  the 


.<«., 


I 


mm 


structures  of  the  lid. 

Lymphatics. — These  form 
two  anastomosing  plexuses, 
one  anterior,  the  other  pos- 
terior to  the  tarsus. 

Nerves. — The  nerves  form 
plexuses  in  the  substance  of 
the  lid.  From  these,  terminal 
fibrils  pass  to  the  various  struct- 
ures of  the  lid.  Many  of  the 
fibres  end  freely  in  fine  net- 
works around  the  tarsal  glands, 
upon  the  blood-vessels,  and  in 
the  epithelium  of  the  conjunc- 
tiva. Other  fibres  terminate 
in  end-bulbs  which  are  espe- 
cially numerous  at  the  margin 
of  the  lid. 

Development  of  the  Eye. 

The  eyes  begin  their  de- 
velopment very  early  in  em- 
bryonic life.  As  optic  depres- 
sions they  are  visible  even 
before  the  closure  of  the  med- 
ullary groove.  As  a  result  of 
the  closure  of  this  groove,  the 
optic  depressions  are  trans- 
formed into  the  optic  vesicles. 
The  connection  between  ves- 
icle and  brain  now  becomes  narrowed  so  that  the  two  are  connected 
only  by  the  thin  optic  stalk.  The  surface  of  the  optic  vesicle  be- 
comes firmly  adherent  to  the  epidermis  and  as  a  result  of  prolif- 
eration of  ectodermic  cells  at  this  point  is  pushed  inward  (invag- 
inated),    forming    the    optic    cup.       The    invagination    of  the    optic 


FIG.  278.— Vertical  Section  through  Upper  Eyelid. 
(Waldeyer.)  a,  Skin  ;  fi,  orbicularis  muscle;  fi\ 
ciliary  bundle  of  muscle;  c,  involuntary  muscle 
of  eyelid  ;  d,  conjunctiva  ;  e,  tarsus  containing 
Meibomian  glands;/",  duct  of  Meibomian  gland  ; 
£■,  sebaceous  gland  with  duct  lying  near  eye- 
lashes ;  //,  eyelashes  ;  i,  small  hairs  in  outer  skin  ; 
J,  sweat  glands  ;  fc,  posterior  tarsal  glands. 


43?  THE   ORGANS. 

vesicle  extends  also  to  the  stalk,  the  sulcus  in  the  latter  being  known 
as  the  choroid  fissure.  The  latter  serves  for  the  introduction  of 
mesenchyme  and  the  development  of  the  hyaloid  retinal  artery. 
Three  distinct  parts  may  now  be  distinguished  in  the  developing  eye, 
which  at  this  stage  is  known  as  the  secondary  optic  vesicle :  {a)  The 
proliferating  epidermis  which  is  to  form  the  lens;  (/;)  the  more  su- 
perficial of  the  invaginated  layers  which  is  to  become  the  retina;  and 
(c)  the  surrounding  mesodermic  tissue  from  which  the  outer  coats  of 

the  eye  are  to  develop. 

TECHNIC. 

(i)  For  the  study  of  the  general  structures  of  the  eyeball  the  eye  of  some  large 
animal,  such  as  an  ox,  is  most  suitable.  Fix  the  eye  for  about  a  week  in  ten-per- 
cent formalin.  Then  wash  in  water  and  bisect  the  eye  in  such  a  manner  that  the 
knife  passes  through  the  optic-nerve  entrance  and  the  centre  of  the  cornea.  The 
half  eye  should  now  be  placed  in  a  dish  of  water  and  the  structures  shown  in  Fig. 
265  identified  with  the  naked  eye  or  dissecting  lens.  On  removing  the  vitreous 
and  retina,  the  pigmented  epithelium  of  the  latter  usually  remains  attached  to  the 
choroid  from  which  it  may  be  scraped  and  examined  in  water  or  mounted  in  gly- 
cerin. In  removing  the  lens  note  the  lens  capsule  and  the  suspensory  ligament. 
The  lens  may  be  picked  to  pieces  with  the  forceps,  and  a  small  piece,  after  further 
teasing  with  needles,  examined  in  water  or  mounted  in  glycerin  or  eosin-glycerin. 
The  retinal  surface  of  the  choroid  shows  the  iridescent  membrane  of  Bruch.  By 
placing  a  piece  of  the  choroid,  membrane-of-Bruch-side  down,  over  the  tip  of  the 
finger  and  gently  scraping  with  a  knife  in  the  direction  of  the  larger  vessels,  the 
latter  may  be  distinctly  seen.  By  now  staining  the  piece  lightly  with  hematoxylin 
and  strongly  with  eosin,  clearing  in  oil  of  origanum  and  mounting  in  balsam,  the 
choriocapillaris  and  the  layer  of  straight  vessels  become  distinctly  visible  with 
the  low-power  lens.  In  removing  the  choroid  note  the  close  attachment  of  the 
latter  to  the  sclera,  this  being  due  to  the  intimate  association  of  the  fibres  of  the 
lamina  suprachoroidea  and  of  the  lamina  fusca.  If  the  brown  shreds  attached  to 
the  inner  side  of  the  sclera  be  examined,  the  pigmented  connective-tissue  cells  of 
the  sclera  can  be  seen. 

(2)  For  the  study  of  the  liner  structure  of  the  coats  of  the  eye,  a  human  eye  if 
it  is  possible  to  obtain  one,  if  not,  an  eye  from  one  of  the  lower  animals,  should 
be  fixed  in  formalin-Midler's  fluid  (technic  5,  p.  5)  and  hardened  in  alcohol.  (A 
few  drops  of  strong  formalin  injected  by  means  of  a  hypodermic  needle  directly 
into  the  vitreous  often  improves  the  fixation.)  The  eye  should  next  be  divided 
into  quadrants  by  first  carrying  the  knife  through  the  middle  of  the  cornea  and  of 
the  optic-nerve  entrance  and  then  dividing  each  half  into  an  anterior  and  a  poste- 
rior half.  Block  in  celloidin,  cut  the  following  sections,  and  stain  with  ha?matoxy- 
lineosin  (technic  i,  p.  16). 

(ei)  Section  through  the  sclero-corneal  junction,  including  the  ora  serrata, 
ciliary  body,  iris,  and  lens.  Before  attempting  to  cut  this  section  almost  all  of  the 
lens  should  be  picked  out  of  the  block,  leaving  only  a  thin  anterior  and  lateral  rim 
attached  to  the  capsule  and  suspensory  ligament.  The  block  should  then  be  so 
clamped  to  the  microtome  that  the  lens  is  the  last  part  of  the  block  to  be  cut.  The 
above  precautions  are  necessary  on  account  of  the  density  of  the  lens,  making  it 
difficult  to  cut. 


THE   ORGANS   OF  SPECIAL   SENSE.  433 

(b)  Section  through  the  postero-lateral  portion  of  the  eyeball  to  show  struct- 
ure of  sclera,  choroid,  and  retina.  This  section  should  be  as  thin  as  possible  and 
perpendicular  to  the  surface. 

(c)  Section  through  the  entrance  of  the  optic  nerve.  Haematoxylin-picro  acid- 
fuchsin  also  makes  a  good  stain  for  this  section.  It  is  instructive  in  cutting  the 
eye  to  cut  a  small  segment  from  the  optic  nerve  and  to  block  it  with  the  optic- 
nerve  entrance  material  in  such  a  manner  that  it  is  cut  transversely.  In  this  way 
both  longitudinal  and  transverse  sections  of  the  optic  nerve  appear  in  the  same 
section. 

(d)  For  the  study  of  the  neurone  relations  of  the  retina  material  must  be 
treated  by  one  of  the  Golgi  methods  (page  27). 

1 4)  The  connective-tissue  cells  and  cell  spaces  of  the  cornea  may  be  demon- 
strated by  means  of  technics  8  and  9,  page  71. 

(5)  The  different  parts  of  the  lacrymal  apparatus  may  be  studied  by  fixing 
material  in  formalin-Muller's  fluid  and  staining  sections  in  hasmatoxylin-eosin. 

(6)  The  Eyelid.  An  upper  eyelid,  human  if  possible,  should  be  carefully 
pinned  out  on  cork,  skin  side  down,  and  fixed  in  formalin-Muller's  fluid.  Vertical 
sections  should  be  stained  with  hasmatoxylin-eosin  or  with  haematoxylin-picro-acid- 
fuchsin. 

The  Organ  of  Hearing. 

The  organ  of  hearing  comprises  the  external  ear,  the  middle  ear, 
and  the  internal  ear. 

The  External  Ear. 

The  external  ear  consists  of  the  pinna  or  auricle,  the  external 
auditory  canal,  and  the  outer  surface  of  the  tympanic  membrane. 

The  pinna  consists  of  a  framework  of  elastic  cartilage  embedded 
in  connective  tissue  and  covered  by  skin.  The  latter  is  thin  and 
contains  hairs,  sebaceous  glands,  and  sweat  glands. 

The  external  auditory  canal  consists  of  an  outer  cartilaginous  por- 
tion and  an  inner  bony  portion.  Both  are  lined  with  skin  continuous 
with  that  of  the  surface  of  the  pinna.  In  the  cartilaginous  portion  of 
the  canal  the  skin  is  thick  and  the  papillae  are  small.  Hair,  sebaceous 
glands,  and  large  coiled  glands  {ceruminous  glands)  are  present.  The 
last  named  resemble  the  glands  of  Mall  (page  430)  and  are  probably 
modified  sweat  glands.  Their  cells  contain  numerous  fat  droplets 
and  pigment  granules.  They  have  long  narrow  ducts  lined  with  a 
two-layered  epithelium.  In  children  these  ducts  open  into  the  hair 
follicles  ;  in  the  adult  they  open  on  the  surface  near  the  hair  follicles. 
The  secretion  of  these  glands  plus  desquamated  epithelium  consti- 
tutes the  ear  -wax.  In  the  bony  portion  of  the  canal  the  skin  is 
thin,  free  from  glands  and  hair,  and  firmly  adherent  to  the  perios- 
teum. 

28 


434  THE   ORGANS. 

The  tympanic  membrane  (ear  drum)  separates  the  external  ear 
from  the  middle  ear.  It  consists  of  three  layers  :  a  middle  layer  or 
substantia  propria,  an  outer  layer  continuous  with  the  skin  of  the 
external  ear,  and  an  inner  layer  continuous  with  the  mucous  mem- 
brane of  the  middle  ear. 

The  substantia  propria  consists  of  closely  woven  connective-tis- 
sue fibres,  the  outer  fibres  having  a  radial  direction  from  the  head  of 
the  malleus,  the  inner  fibres  having  a  concentric  arrangement  and 
being  best  developed  near  the  periphery. 

The  outer  layer  of  the  tympanic  membrane  is  skin,  consisting  of 
epidermis  and  of  a  thin  non-pap i Hated  corium,  excepting  over  the 
manubrium  of  the  malleus,  where  the  skin  is  thicker  and  papillated. 

The  inner  layer  is  mucous  membrane  and  consists  of  a  stroma  of 
fibro-elastic  tissue  covered  with  a  single  layer  of  low  epithelial  cells. 

Blood-vessels. — Blood  is  supplied  to  the  tympanic  membrane  by 
two  sets  of  vessels,  an  external  set  derived  from  the  vessels  of  the 
external  auditory  meatus  and  an  internal  set  from  the  vessels  of  the 
middle  ear.  These  give  rise  to  capillary  networks  in  the  skin  and 
mucous  membrane  respectively  and  anastomose  by  means  of  perfo- 
rating branches  at  the  periphery  of  the  membrane.  From  the  capil- 
laries the  blood  passes  into  two  sets  of  small  veins,  one  extending 
around  the  periphery  of  the  membrane,  the  other  following  the  handle 
of  the  malleus. 

Lymphatics. — These  follow  in  general  the  course  of  the  blood- 
vessels.     They  are  most  numerous  in  the  outer  layer. 

Nerves. — The  larger  nerves  run  in  the  substantia  propria.  From 
these,  branches  pass  to  the  skin  and  mucous  membrane,  beneath  the 
surfaces  of  which  they  form  plexuses  of  fine  fibres. 

The  Middle  Ear. 

The  middle  ear  or  tympanum  is  a  small  chamber  separated  from 
the  external  ear  by  the  tympanic  membrane  and  communicating  with 
the  pharynx  by  means  of  the  Eustachian  tube.  Its  walls  are  formed 
by  the  surrounding  bony  structures  covered  by  periosteum.  It  is 
lined  with  mucous  membrane  and  contains  the  ear  ossicles  and  their 
ligamentous  and  muscular  attachments.  The  epithelium  is  of  the 
simple  low  cuboidal  type.  In  places  it  may  be  ciliated  and  not  in- 
frequently assumes  a  pseudostratified  character  with  two  layers  of 


THE   ORGANS    OF  SPECIAL   SENSE. 


435 


nuclei.  Beneath  the  epithelium  is  a  thin  stroma  which  contains 
some  diffuse  lymphoid  tissue  and  blends  with  the  dense  underlying 
periosteum.  Small  tubular  glands  are  usually  present,  especially 
near  the  opening  of  the  Eustachian  tube. 

The  fenestra  rotunda  is  covered  by  the  secondary  tympanic  mem- 
brane. This  consists  of  a  central  lamina  of  connective  tissue  covered 
on  its  tympanic  side  by  part  of  the  mucous  membrane  of  that  cham- 
ber, on  the  opposite  side  by  a  single  layer  of  endothelium. 

The  ossicles  are  composed  of  bone  tissue  arranged  in  the  usual 
systems  of  lamellae.  The  stapes  alone  contains  a  marrow  cavity. 
Over  their  articular  surfaces  the  ossicles  are  covered  by  hyaline  car- 
tilage. 

The  Eustachian  Tube. — This  is  a  partly  bony,  partly  cartilaginous 
canal  lined  with  mucous  membrane.  The  epithelium  of  the  latter  is 
of  the  stratified  columnar  ciliated  variety  consisting  of  two  layers  of 
cells.  In  the  bony  portion  of  the  tube  the  stroma  is  small  in  amount 
and  intimately  connected  with  the  periosteum.  In  the  cartilaginous 
portion  the  stroma  is  thicker  and  contains,  especially  near  the  pharyn- 
geal opening,  lymphoid  tissue  and  simple  tubular  mucous  glands. 

The  Internal  Ear. 


Amjpvllaif- 


The  internal  ear  consists  of  a  complex  series  of  connected  bony 
walled  chambers  and  passages  containing  a  similar-shaped  series  of 
membranous  sacs  and  tubules. 
These  are  known  respectively  as 
the  osseous  labyrinth  and  the 
membranous  la  by  r  i  n  t  h.  Be- 
tween the  two  is  a  lymph  space, 
which  contains  the  so-called 
perilymph^  while  within  the 
membranous  labyrinth  is  a  sim- 
ilar fluid,  the  endolymph. 

The  bony  labyrinth  consists 
of  a  central  chamber,  the  ves- 
tibule,   from  which  are  given  Off    FIG.  -jg.-The   Bony  Labyrinth. 

the  three  semicircular  canals  and 

the  cochlea.      The  vestibule  is  separated  from  the  middle  ear  by  a 

plate  of  bone  in  which  are  two  openings,  the  fenestra  ovalis  and  the 


Ampulla 


(Heitz- 


436 


THE   ORGANS. 


fenestra  rotunda.  Just  after  leaving  the  vestibule  each  canal  pre- 
sents a  dilatation,  the  ampulla.  As  each  canal  has  a  return  opening 
into  the  vestibule  and  as  the  anterior  and  posterior  canals  have  a 
common  return  opening  (the  canalis  communis),  there  are  five  open- 


FlG.  280. — Diagram  of  the  Perilymphatic  and  Endolymphatic  Spaces  of  the  Inner  Ear.  (Tes- 
tut.)  Endolymphatic  spaces  in  gray  ;  perilymphatic  spaces  in  black.  /,  Utricle;  2,  sac- 
cule ;  j,  semicircular  canals  ;  4,  cochlear  canal  ;  j,  endolymphatic  duct  ;  6,  subdural  endo- 
lymphatic sac  ;  7,  canalis  reuniens;  S,  scala  tympani ;  9,  scala  vestibuli  ;  jo,  their  union  at 
the  helicotrema;  //,  aqueduct  of  the  vestibule;  12.  aqueduct  of  the  cochlea;  /^perios- 
teum :  14,  dura  mater  ;  jj,  stapes  in  fenestra  ovalis  ;  ib,  fenestra  rotunda  and  secondary 
tympanic  membrane. 


ings  from  the  vestibule  into  the  semicircular  canals  (Fig.  279). 
The  bony  labyrinth  is  lined  with  periosteum,  covered  by  a  single 
layer  of  endothelial  cells. 

The  Vestibule  and  the  Semicircular  Canals. — In  the  vestibule 
the  membranous  labyrinth  is  subdivided  into  two  chambers,  the  sac- 
cule and  the  utricle,  which  are  connected  by  the  utriculosaccular 
duct.  From  the  latter  is  given  off  the  endolymphatic  duct  which 
communicates  through  the  aqueduct  of  the  vestibule,  with  a  subdural 
lymph  space,  the  endolymphatic  sac.  The  saccule  opens  by  means 
of  the  ductus  reuniens  into  the  cochlea,  while  the  utricle  opens  into 
the  ampullseof  the  semicircular  canals.  The  saccule  and  utricle  only 
partly  fill  the  vestibule,  the  remaining  space,  crossed  by  fibrous  bands 
and  lined  with  endothelium,  constituting  the  perilymphatic  space. 


THE   ORGANS    OF  SPECIAL    SENSE. 


437 


Saccule  and  Utricle. — The  walls  of  the  saccule  and  of  the 
utricle  consist  of  fine  fibro-elastic  tissue  supporting  a  thin  basement 
membrane,  upon  which  rests  a  single  layer  of  low  epithelial  cells.  In 
the  wall  of  each  chamber  is  an  area  of  special  nerve  distribution,  the 
macula  acustica.  Here  the  epithelium  changes  to  high  columnar 
and  consists  of  two  kinds  of  cells,  sustentacular  and  neuro-epithelial. 
The  sustentacular  cells  are  long,  irregular,  nucleated  cylinders,  narrow 
in  the  middle,  widened  at  each  end,  the  outer  end  being  frequently 
split  and  resting  upon  the  basement  membrane.  The  neuro-epithelial 
cells  or  "hair  cells"  are  short  cylinders  which  extend  only  about  half- 
way through  the  epithelium.  The  basal  end  of  the  cell  is  the  larger 
and  contains  the  oval  nucleus.  The  surface  of  the  cell  is  provided 
with  a  cuticular  margin  from  which  project  several  long  hair- like 
processes,  the  auditory  hairs.  Small  crystals  of  calcium  carbonate 
are  found  on  the  surfaces  of  the  hair  cells.  These  are  known  as 
otoliths  and  are  embedded  in  a  soft  substance,  the  otolithic  membrane. 
The  hair  cells  are  the  neuro-epithelial  end-organs  of  the  vestibular 
division  of  the  auditory  nerve  and  are,  therefore,  closely  associated 
with  the  nerve  fibres.     The  latter  on  piercing  the  basement  mem- 


FlG.  281.— Diagram  of  the  Right  Membranous  Labyrinth.  (Testut.)  /,  Utricle;  2,  superior 
semicircular  canal  ;  3,  posterior  semicircular  canal  ;  4,  external  semicircular  canal  ;  j,  sac- 
cule ;  6,  endolymphatic  duct  ;  7  and  7',  canals  connecting  utricle  and  saccule  respectively 
with  the  endolymphatic  duct  ;  S,  endolymphatic  sac;  g.  cochlear  duct;  </,  its  vestibular 
cul-de-sac  ;  <?",  its  terminal  cul-de-sac;  /o,  canalis  reuniens. 


brane  lose  their  medullary  sheaths  and  split  up  into  several  small 
branches,  which  form  a  horizontal  plexus  between  the  basement 
membrane  and  the  bases  of  the  hair  cells.  From  this  plexus  are 
given  off  fibrils  which  end  freely  between  the  hair  cells. 


433 


THE   ORGANS. 


Semicircular  Canals. — The  walls  of  the  semicircular  canals  are 
similar  in  structure  to  the  walls  of  the  saccule  and  utricle;  they  also 
bear  a  similar  relation  to  the  walls  of  the  bony  canal.  Along  the 
concavity  of  each  canal  the  epithelium  is  somewhat  higher,  forming 


Fig.  2S2.— The  Membranous  Labyrinth  from  the  Right  Internal  Ear  of  a  Human  Embryo  at 
the  Fifth  Month  ;  seen  from  the  Medial  Side.  (After  Retzius,  from  Barker.)  /-j,  Utricle ; 
2,  utricular  recess ;  j,  macula  acustica  of  utricle  ;  4,  posterior  sinus  ;  j,  superior  sinus  ;  6, 
7,  <?,  superior,  lateral,  and  posterior  ampullae  ;  g,  10,  //,  superior,  posterior,  and  lateral 
semicircular  canals  ;  12,  widened  mouth  of  lateral  semicircular  canal  opening  into  the 
utricle;  /j,  saccule;  14,  macula  acustica  of  the  saccule;  /j,  endolymphatic  duct;  16, 
utriculosaccular  duct ;  77,  ductus  reuniens  ;  /<?,  vestibular  cul-de-sac  of  cochlear  duct ;  /<?, 
cochlear  duct ;  20.  facial  nerve  ;  21-24,  auditory  nerve  ;  2/,  its  vestibular  branch  ;  22,  sac- 
cular branch;  2j,  branch  to  inferior  ampulla;  24,  cochlear  branch;  25,  distribution  of 
cochlear  branch  within  the  bony  spiral  lamina. 

the  raphe.  In  each  ampulla  is  a  crista  acustica,  the  structure  of 
which  is  similar  to  that  of  the  maculae  of  the  saccule  and  utricle. 
With  the  adjoining  high  columnar  cells,  this  forms  the  so-called 
semilunar  fold.  As  in  the  case  of  the  maculae  the  hair  cells  have 
otoliths  upon  their  surfaces,  the  otolithic  membrane  here  forming  a 
sort  of  dome  over  the  hair  cells  known  as  the  cupula. 

The  Cochlea. — The  bony  cochlea  consists  of  a  conical  axis,  the 
modiolus,  around  which  winds  a  spiral  bony  canal.  This  canal  in 
man  makes  about  two  and  one-half  turns,  ending  at  the  rounded  tip 
of  the  cochlea  or  cupola.  Projecting  from  the  modiolus  partly  across 
the  bony  canal  of  the  cochlea  is  a  plate  of  bone,  the  bony  spiral 
lamina  (Fig.  283,  x).  This  follows  the  spiral  turns  of  the  cochlea, 
ending  at  the  cupola  in  a  hook-shaped  process,  the  hamulus.  Along 
the  outer  side  of  the  canal,  opposite  the  bony  spiral  lamina,  is  a  pro- 
jection of  thickened  periosteum,  the  spiral  ligament  (Fig.  283,  //). 
A  connective-tissue  membrane,  the  membranous  spiral  lamina  (Fig. 


THE  ORGANS   OF  SPECIAL   SENSE. 


439 


283,  s),  crosses  the  space  intervening  between  the  spiral  ligament  and 
the  bony  spiral  lamina,  thus  completely  dividing  the  bony  canal  of 
the  cochlea  into  two  parts,  an  upper,  scala  vestibuli  (Fig.  283,  /)  and 
a  lower,  scala  tympani  (Fig.  283,  k).  These  are  perilymphatic 
spaces,  the  scala  vestibuli  communicating  with  the  perilymph  space 
of  the  vestibule,  the  scala  tympani  communicating  with  the  perivas- 
cular lymph  spaces  of  the  veins  of  the  cochlear  duct.  The  scala  ves- 
tibuli and  the  scala  tympani  communicate  with  each  other  in  the 
cupola  by  means  of  a  minute  canal,  the  helicotrema. 

The  Cochlear  Duct  {Membranous  Cochlea  or  Scala  Media). — 
This  is  a  narrow,  membranous  tube  lying  near  the  middle  of  the 


Fig.  2S3. — Section  through  a  Single  Turn  of  the  Cochlea  of  a  Guinea-pig.  (Bohm  and  von 
Davidoff.)  <7,  Bone  of  cochlea;  /,  scala  vestibuli;  Dc,  scala  media  or  cochlear  duct;  k, 
scala  tympani ;  b,  membrane  of  Reissner  ;  d,  membrana  tectoria  or  membrane  of  Corti ; 
f,  spiral  prominence  ;  g;  organ  of  Corti ;  A,  spiral  ligament ;  i\  basilar  membrane  (outer 
portion — zona  pectinata — covered  by  cells  of  Claudius);  z,  stria  vascularis;  v.  external 
spiral  sulcus;  r,  crista  basilaris  ;  s,  membranous  spiral  lamina;  x,  bony  spiral  lamina; 
m,  spiral  limbus  ;  ;/,  internal  spiral  sulcus  ;  o,  medullated  peripheral  processes  (dendrites) 
of  cells  of  spiral  ganglion  passing  to  the  organ  of  Corti;  /,  spiral  ganglion;  q.  blood- 
vessel. 


bony  cochlear  canal  and  following  its  spiral  turns  from  the  vestibule, 
where  it  is  connected  with  the  saccule  through  the  canalis  reuniens, 


440  THE   ORGAXS. 

to  its  blind  ending  in  the  cupola.  It  is  triangular  in  shape  on  trans- 
verse section,  thus  allowing  a  division  of  its  walls  into  upper,  outer, 
and  lower  (Fig.  283,  Dc). 

The  upper  or  vestibular  wall  is  formed  by  the  thin  membrane  of 
Reissner  (Fig.  283,  b)  which  separates  the  cochlear  duct  from  the 
scala  vestibuli.  The  membrane  consists  of  a  thin  central  lamina  of 
connective  tissue  covered  on  its  vestibular  side  by  the  vestibular  en- 
dothelium, on  its  cochlear  side  by  the  epithelium  of  the  cochlea. 

The  outer  wall  of  the  cochlear  duct  is  formed  by  the  spiral  liga- 
ment, which  is  a  thickening  of  the  periosteum.  The  outer  part  of 
the  spiral  ligament  consists  of  dense  fibrous  tissue,  its  projecting 
part  of  more  loosely  arranged  tissue.  From  it,  two  folds  project 
slightly  into  the  duct.  One,  the  crista  basilaris  (Fig.  283,  ;-),  serves 
for  the  attachment  of  the  membranous  spiral  lamina;  the  other,  the 
spiral  prominence  (Fig.  283,  f),  contains  several  small  veins.  Be- 
tween the  two  projections  is  a  depression,  the  external  spiral  sulcus 
(Fig.  283,  7').  That  part  of  the  spiral  ligament  between  the  spiral 
prominence  and  the  attachment  of  Reissner's  membrane  is  known  as 
the  stria  vascularis  (Fig.  283,  z).  It  is  lined  with  granular  cuboidal 
epithelial  cells,  which,  owing  to  the  absence  of  a  basement  mem- 
brane, are  not  sharply  separated  from  the  underlying  connective  tis- 
sue. For  this  reason  the  capillaries  extend  somewhat  between  the 
epithelial  cells,  giving  the  unusual  appearance  of  a  vascular  epithe- 
lium. 

The  lower  or  tympanic  wall  of  the  cochlear  duct  has  an  extremely 
complex  structure.  Its  base  is  formed  by  the  already  mentioned  bony 
and  membranous  division  wall  between  the  scala  media  and  the  scala 
tympani  (bony  spiral  lamina  and  membranous  spiral  lamina). 

The  bony  spiral  lamina  has  been  described  (page  438). 

The  membranous  spiral  lamina  consists  of  a  substantia  propria  or 
basilar  membrane,  its  tympanic  covering,  and  its  cochlear  covering. 

The  basilar  membrane  (Fig.  283)  is  a  connective-tissue  mem- 
brane composed  of  fine  straight  fibres  which  extend  from  the  bony 
spiral  lamina  to  the  spiral  ligament.  Among  the  fibres  are  a  few 
connective-tissue  cells.  On  either  side  of  the  fibre  layer  is  a  thin, 
apparently  structureless  membrane. 

The  tympanic  covering  of  the  basilar  membrane  consists  of  a  thin 
layer  of  connective  tissue — an  extension  of  the  periosteum  of  the 
spiral  lamina — covered  over  by  a  single  layer  of  flat  endothelial  cells. 


THE   ORGANS   OF  SPECIAL   SENSE. 


441 


The  cochlear  covering  of  the  basilar  membrane  is  epithelial. 
Owing  to  the  marked  difference  in  the  character  of  the  epithelium, 
the  basilar  membrane  is  divided  into  an  outer  portion,  the  zona 
pectinata  (Fig.  283,  i)  and  an  inner  portion,  the  zona  tecta  (Fig. 
283,  s).  The  epithelium  of  the  former  is  of  the  ordinary  columnar 
type ;  that  of  the  latter  is  the  highly  differentiated  neuro-epithelium 
of  Corti's  organ. 

The  Organ  of  Corti. — The  spiral  organ  or  the  organ  of  Corti 
(Fig.  283,  g,  and  Fig.  284)  is  a  neuro-epithelial  structure  running 
the  entire  length  of  the  cochlear  canal  with  the  exception  of  a  short 


limbus 


mcmbrana  tectoria 


''"-'■■"■Z££'jQ'.& 


nerve  fibres 


inner  rod    vas    basilar  outer    cells  of  Deiters 

stpiialc    membrane     rod 


Fig.  284. — Semidiagrammatic  Representation  of  the  Organ  of  Corti  and  Adjacent  Structures. 
(Merkel-Henle.)  a.  Cells  of  Hensen  ;  d,  cells  of  Claudius;  c,  internal  spiral  sulcus;  x, 
Nuel's  space.  The  nerve  fibres  (dendrites  of  cells  of  the  spinal  ganglion)  are  seen  pass- 
ing to  Corti's  organ  through  openings  (foramina  nervosa)  in  the  bony  spiral  lamina. 
The  black  dots  represent  longitudinally-running  branches,  one  bundle  lying  to  the  inner 
side  of  the  inner  pillar,  a  second  just  to  the  outer  side  of  the  inner  pillar  within  Corti's 
tunnel,  the  third  beneath  the  outer  hair  cells. 


distance  at  either  end.  It  rests  upon  the  membranous  portion  of  the 
spiral  lamina,  and  consists  of  a  complex  arrangement  of  four  different 
kinds  of  epithelial  cells.  These  are  known  as:  (1)  pillar  cells,  (2) 
hair  cells,  (3)  Deiter's  cells,  and  (4)  Hensen's  cells  (Fig.  284). 

(1)  The  pillar  cells  are  divided  into  outer  pillar  cells  and  inner 
pillar  cells.  They  are  sustentacular  in  character.  Each  cell  con- 
sists of  a  broad  curved  protoplasmic  base  which  contains  the  nucleus, 
and  of  a  long-drawn-out  shaft  or  pillar  which  probably  represents  a 
highly  specialized  cuticular  formation.  The  end  of  the  pillar  away 
from  the  base  is  known  as  the  head.     The  head  of  the  outer  pillar 


442  THE   ORGANS. 

presents  a  convexity  on  its  inner  side,  which  fits  into  a  corresponding 
concavity  on  the  head  of  the  inner  pillar,  the  heads  of  opposite  pillars 
thus  "articulating"  with  each  other.  From  their  articulation  the 
pillars  diverge,  so  that  their  bases  which  rest  upon  the  basilar  mem- 
brane are  widely  separated.  There  are  thus  formed  by  the  pillars  a 
series  of  arches  known  as  Corti  s  arches,  enclosing  a  triangular  canal, 
Corti  s  tunnel.  This  canal  is  filled  with  a  gelatinous  substance  and 
crossed  by  delicate  nerve  fibrils.  As  the  outer  pillar  cells  are  the 
larger,  they  are  fewer  in  number,  the  estimated  number  in  the  human 
cochlea  being  about  forty- five  hundred  of  the  outer  cells  and  about 
six  thousand  of  the  inner  cells. 

(2)  The  hair  cells  or  auditory  cells  lie  on  either  side  of  the  arches 
of  Corti,  and  are  thus  divided  into  inner  hair  cells  and  outer  hair 
cells.  Both  inner  and  outer  hair  cells  are  short,  cylindrical  elements 
which  do  not  extend  to  the  basilar  membrane.  Each  cell  ends  below 
in  a  point,  while  from  its  free  surface  are  given  off  a  number  of  fine 
stiff  hairs. 

The  inner  hair  cells  lie  in  a  single  layer  against  the  inner  side  of 
the  inner  pillar  cells,  one  hair  cell  resting  upon  about  every  two  pil- 
lars. 

The  outer  hair  cells  lie  in  three  or  four  layers  to  the  outer  side 
of  the  outer  pillar  cells,  being  separated  from  one  another  by  susten- 
tacular  cells,  the  cells  of  Deiter,  so  that  no  two  hair  cells  come  in 
contact. 

(3)  Deiter  s  Cells  (Fig.  284). — These  like  the  pillar  cells  are  sus- 
tentacular.  Their  bases  rest  upon  the  basilar  membrane,  where  they 
form  a  continuous  layer.  Toward  the  surface  they  become  separated 
from  one  another  by  the  hair  cells.  The  long  slender  portions  of  the 
Deiter's  cells,  which  pass  in  between  the  hair  cells,  are  known  as 
phalangeal  processes.  Between  the  innermost  of  the  outer  hair 
cells  and  the  outer  pillar  is  a  space  known  as  NucT  s  space  (Fig. 
284,  a-). 

(4)  Ilcnsciis  Cells  (Fig.  284,  a). — These  are  sustentacular  cells, 
which  form  about  eight  rows  to  the  outer  side  of  the  outermost  Dei- 
ter's cells.  These  cells  form  the  outer  crest  of  Corti's  organ  and 
consequently  have  a  somewhat  radial  disposition,  their  free  surfaces 
being  broad,  their  basal  ends  narrow.  They  decrease  in  height  from 
within  outward,  and  at  the  end  of  Corti's  organ  become  continuous 
with  the  cells  of  Claudius  (Fig.  284,  /;),  the  name  given  to  the  coch- 


THE  ORGANS   OF  SPECIAL  SENSE.  443 

lear  epithelium  covering  the  basal  membrane  to  the  outer  side  of 
Corti's  organ. 

The  phalangeal  processes  of  the  Deiter's  cells  are  cemented  to- 
gether and  to  the  superficial  parts  of  the  outer  pillars  in  such  a  man- 
ner as  to  form  a  sort  of  cuticular  membrane,  the  lamina  reticularis, 
through  which  the  heads  of  the  outer  hair  cells  project.  This  mem- 
brane also  extends  out  as  a  cuticula  over  the  cells  of  Hensen  and  of 
Claudius. 

The  Mcmbrana  Tcctoria. — This  is  a  peculiar  membranous  struct- 
ure attached  to  a  projection  of  the  bony  spiral  lamina  known  as  the 
spiral  limbus  (Fig.  284),  the  concavity  beneath  its  attachment  being 
the  internal  spiral  sulcus  (Fig.  284,  c).  The  membrane  is  non-nu- 
cleated and  shows  fine  radial  striations.  It  bridges  over  the  internal 
spiral  sulcus  and  ends  in  a  thin  margin,  which  rests  upon  Corti's 
organ  just  at  the  outer  limit  of  the  outer  hair  cells. 

Blood-vessels. — The  arteries  consist  of  two  small  branches  of  the 
auditory — one  to  the  bony  labyrinth,  the  other  to  the  membranous 
labyrinth.  The  latter  divides  into  two  branches — a  vestibular  and  a 
cochlear.  The  vestibular  artery  accompanies  the  branches  of  the 
auditory  nerve  to  the  utricle,  saccule,  and  semicircular  canals.  It 
supplies  these  parts,  giving  rise  to  a  capillary  network,  which  is 
coarse  meshed  except  in  the  cristas  and  maculae,  where  the  meshes 
are  fine.  The  cochlear  artery  also  starts  out  in  company  with  the 
auditory  nerve,  but  accompanies  it  only  to  the  first  turn  of  the  coch- 
lea. Here  it  enters  the  modiolus  where  it  gives  off  several  much 
coiled  branches,  the  glomerular  arteries  of  the  cochlea.  Branches 
from  these  pierce  the  vestibular  part  of  the  osseous  spiral  lamina  and 
supply  the  various  structures  of  the  cochlear  duct.  The  veins  ac- 
company the  arteries,  but  reach  the  axis  of  the  modiolus  through 
foramina  in  the  tympanic  part  of  the  bony  spiral  lamina. 

Lymphatics. — The  scala  media  contains  endolymph  and  is  in 
communication  with  the  subdural  lymph  spaces  by  means  of  the  en- 
dolymphatic duct,  the  endolymphatic  sac,  and  minute  lymph  channels 
connecting  the  latter  with  the  subdural  spaces.  The  perilymph 
spaces — scala  tympani  and  scala  vestibuli — are  connected  with  the 
pial  lymph  spaces  by  means  of  the  perilymphatic  duct.  Lymph 
spaces  also  surround  the  vessels  and  nerves.  These  empty  into  the 
pial  lymphatics. 

Nerves. — The  vestibular  branch  of  the  auditory  nerve  divides  into 


444  THE   ORGANS. 

branches  which  supply  the  saccule,  utricle,  and  semicircular  canals, 
where  they  end  in  the  maculae  and  crista?  as  described  on  page  437. 
The  ganglion  of  the  vestibular  branch  is  situated  in  the  internal 
auditory  meatus.  The  cochlear  branch  of  the  auditory  nerve  enters 
the  axis  of  the  modiolus,  where  it  divides  into  a  number  of  branches 
which  pass  up  through  its  central  axis.  From  these,  numerous  fibres 
radiate  to  the  bony  spiral  laminae,  in  the  bases  of  which  they  enter 
the  spiral  ganglia  (Fig.  283,  />). 

The  cells  of  the  spiral  ganglia  are  peculiar,  in  that  while  of  the 
same  general  type  as  the  spinal  ganglion  cell  they  maintain  their 
embryonic  bipolar  condition  (see  page  347)  throughout  life.  Their 
axones  follow  the  already  described  course  through  the  modiolus  and 
thence  through  the  internal  auditory  meatus  to  their  terminal  nuclei 
in  the  medulla  (see  page  383).  Their  dendrites  become  medullated 
like  the  dendrites  of  the  spinal  ganglion  cells  and  pass  outward  in 
bundles  in  the  bony  spiral  laminae  (Fig.  283,  0,  and  Fig.  284). 
From  these  are  given  off  branches  which  enter  the  tympanic  portion 
of  the  lamina,  where  they  lose  their  medullary  sheaths  and  pass 
through  the  foramina  nervosa  (minute  canals  in  the  tympanic  part  of 
the  spiral  lamina)  to  their  terminations  in  the  organ  of  Corti.  In 
the  latter  the  fibres  run  in  three  bundles  parallel  to  Corti's  tunnel. 
One  bundle  lies  just  inside  the  inner  pillar  beneath  the  inner  row  of 
hair  cells  (Fig.  284).  A  second  bundle  runs  in  the  tunnel  to  the 
outer  side  of  the  inner  pillar  (Fig.  284).  The  third  bundle  crosses 
the  tunnel  (tunnel-fibres)  and  turns  at  right  angles  to  run  between 
the  cells  of  Deiter  beneath  the  outer  hair  cells  (Fig.  284).  From 
all  of  these  bundles  of  fibres  are  given  off  delicate  terminals  which 
end  on  the  hair  cells. 

Development  of  the  Ear. 

The  essential  auditory  part  of  the  organ  of  hearing,  the  mem- 
branous labyrinth,  is  of  ectodermic  origin.  This  first  appears  as  a 
thickening  followed  by  an  invagination  of  the  surface  ectoderm  in 
the  region  of  the  posterior  cerebral  vesicle.  This  is  known  as  the 
auditory  pit.  By  closure  of  the  lips  of  this  pit  and  growth  of  the 
surrounding  mesodermic  tissue  is  formed  the  otic  vesicle-or  otocyst, 
which  is  completely  separated  from  the  surface  ectoderm.  Diver- 
ticula soon  appear  passing  off  from  the  otic  vesicle.      These  are  three 


THE   ORGANS   OF  SPECIAL   SENSE.  445 

in  number  and  correspond  respectively  to  the  future  endolymphatic 
duct,  the  cochlear  duct  and  the  membranous  semicircular  canals. 
Within  the  saccule,  utricle,  and  ampullae  special  differentiations  of 
the  lining  epithelium  give  rise  to  the  maculae  and  cristas  acusticae. 
Of  the  cochlear  duct  the  upper  and  lateral  walls  become  thinned  to 
form  Reissner's  membrane  and  the  epithelium  of  the  outer  wall, 
while  the  lower  wall  becomes  the  basilar  membrane,  its  epithelium 
undergoing  an  elaborate  specialization  to  form  the  organ  of  Corti. 

Of  the  cochlea,  only  the  membranous  cochlear  duct  develops  from 
the  otic  vesicle ;  the  scala  vestibuli,  scala  tympani,  and  bony  cochlea 
developing  from  the  surrounding  mesoderm.  The  mesodermic  con- 
nective tissue  at  first  completely  fills  in  the  space  between  the  coch- 
lear duct  and  the  bony  canal.  Absorption  of  this  tissue  takes  place, 
resulting  in  formation  of  the  scala  tympani  and  scala  vestibuli. 

During  the  differentiation  of  the  above  parts  a  constriction  ap- 
pears in  the  body  of  the  primitive  otic  vesicle.  This  results  in  the 
incomplete  septum  which  divides  the  utricle  from  the  saccule. 

The  middle  ear  is  formed  from  the  upper  segment  of  the  pharyn- 
geal groove,  the  lower  segment  giving  rise  to  the  Eustachian  tube. 

The  external  ear  is  developed  from  the  ectoderm  of  the  first 
branchial  cleft  and  adjacent  branchial  arches.  The  tympanic  mem- 
brane is  formed  from  the  mesoderm  of  the  first  branchial  arch,  its 
outer  covering  being  of  ectodermic,  its  inner  of  entodermic  origin. 

TECHNIC. 

(i)  For  the  study  of  the  general  structure  of  the  pinna  and  walls  of  the  exter- 
nal auditory  meatus,  material  may  be  fixed  in  formalin-Midler's  fluid  (technic  5. 
p.  5)  and  sections  stained  with  haematoxylin-eosin  (technic  1.  p.  16).  In  sections 
of  the  wall  of  the  cartilaginous  meatus  the  ceruminous  glands  may  be  studied, 
material  from  children  and  from  new-born  infants  furnishing  the  best  demonstra- 
tions of  these  glands. 

(2)  For  the  study  of  the  inner  ear  the  guinea-pig  is  most  satisfactory  on  account 
of  the  ease  with  which  the  parts  may  be  removed.  Remove  the  cochlea  of  a 
guinea-pig  with  as  much  as  possible  of  the  vestibule  and  semicircular  canals  and 
fix  in  Flemming*s  fluid  (technic  7.  p.  6).  A  small  opening  should  be  made  in  the 
first  turn  of  the  cochlea  in  order  to  allow  the  fixative  to  enter  the  canal.  After 
forty-eight  hours  the  cochlea  is  removed  from  the  fixative  and  hardened  in  graded 
alcohols  (page  7).  The  bone  is  next  decalcified,  either  by  one  of  the  methods  men- 
tioned on  page  8  or  in  saturated  alcoholic  solution  of  picric  acid.  If  one  of  the 
aqueous  decalcifying  fluids  is  used,  care  must  be  taken  to  carry  the  material 
through  graded  alcohols.  Embed  in  celloidin  or  paraffin,  cut  sections  through 
the  long  axis  of  the  modiolus,  through  the  utricle  and  saccule,  and  through  the 
semicircular  canals.     Stain  with  ha?matoxvlin-eosin  and  mount  in  balsam. 


446 


THE   ORGANS. 


(3)  The  neurone  relations  of  the  crista?,  maculae,  and  cochlear  duct  can  be 
demonstrated  only  by  means  of  the  Golgi  method.  The  ear  of  a  new-born  mouse 
or  guinea-pig  furnishes  good  material.  The  cochlea  together  with  some  of  the 
base  of  the  skull  should  be  removed  and  treated  by  the  Golgi  rapid  method  (page 
27).  Sections  should  be  thick  and  must  of  course  be  cut  through  undecalcified 
bone.     Good  results  are  difficult  to  obtain. 

The  Organ  of  Smell. 

The  olfactory  organ  consists  of  the  olfactory  portion  of  the  nasal 
mucosa.  In  this  connection  it  is,  however,  convenient  to  describe 
briefly  the  olfactory  bulb  and  the  olfactory  tract. 

The  Olfactory  Mucosa. — This  has  been  described  (page  237). 
The  peculiar  olfactory  cells  there  described  are  not  neuro-epithelium 
but  are  analogs  of  the  spinal  ganglion  cell,  being  the  only  example 


FIG.  285.— Diagram  of  Structure  of  Olfactory  Mucosa  and  Olfactory  Bulb.  (Ramon  y 
Cajal.)  be,  Bipolar  cells  of  olfactory  mucosa;  sm,  submucosal  etlim,  cribriform  plate 
of  ethmoid;  a,  layer  of  olfactory  fibres;  off,  olfactory  glomeruli;  me,  mitral  cells; 
ep,  epithelium  of  olfactory  ventricle. 

in  man  of  the  peripherally  placed  ganglion  cell  found  in  certain  lower 
animals.  Each  cell  sends  to  the  surface  a  short  dendrite  which  ends 
in  several  short,  stiff,  hair-like  processes.  From  its  opposite  end 
each  cell  gives  off  a  longer  centrally  directed  process  (axone),  which 
as  a  fibre  of  one  of  the  olfactory  nerves  passes  through  the  cribriform 


THE   ORGANS    OF  SPECIAL   SENSE.  447 

plate  of  the  ethmoid  (Fig.  285,  etJiui)  to  its  terminal  nucleus  in  the 
olfactory  bulb  (Fig.  285). 

The  Olfactory  Bulb. — This  is  a  somewhat  rudimentary  structure 
analogous  to  the  much  more  prominent  olfactory  brain  lobe  of  some 
of  the  lower  animals.  It  consists  of  both  gray  matter  and  white 
matter  arranged  in  six  fairly  distinct  layers.  These  from  below  up- 
ward are  as  follows:  (a)  The  layer  of  olfactory  fibres;  (I?)  the  layer 
of  glomeruli;  (c)  the  molecular  layer;  (d)  the  layer  of  mitral  cells  ; 
(f)  the  granule  layer;  (/)  the  layer  of  longitudinal  fibre  bundles. 
Through  the  centre  of  the  last-named  layer  runs  a  band  of  neuroglia 
which  represents  the  obliterated  lumen  of  the  embryonal  lobe.  The 
relations  of  these  layers  to  the  olfactory  neurone  system  are  as  fol- 
lows : 

The  layer  of  olfactory  fibres  (Fig.  285,  a)  consists  of  a  dense 
plexiform  arrangement  of  the  axones  of  the  above-described  olfactory 
cells.  From  this  layer  the  axones  pass  into  the  layer  of  olfactory 
glomeruli  where  their  terminal  ramifications  mingle  with  the  den- 
dritic terminals  of  cells  lying  in  the  more  dorsal  layers,  to  form  dis- 
tinctly outlined  spheroidal  or  oval  nerve-fibre  nests,  the  olfactory 
glomeruli  (Fig.  285,  og).  The  latter  mark  the  ending  of  neurone 
system  No.  I.  of  the  olfactory  conduction  path. 

The  molecular  layer  contains  both  small  nerve  cells  and  large 
nerve  cells.  These  send  their  dendrites  into  the  olfactory  glomeruli. 
The  smaller  cells  belong  to  Golgi  Type  II.  (see  page  106)  and  appear 
to  be  association  neurones  between  adjacent  glomeruli.  The  axones 
of  the  larger  cells,  the  so-called  brush  cells,  become  fibres  of  the 
olfactory  tract. 

Of  the  mitral  cells  (Fig.  285,  me),  the  main  dendrites  end  in  the 
olfactory  glomeruli,  while  their  axones,  like  those  of  the  brush  cells, 
become  fibres  of  the  olfactory  tract. 

In  addition  to  the  fibres  which  pass  through  it  (axones  of  mitral 
and  of  brush  cells),  the  granular  layer  contains  numerous  nerve  cells. 
Many  of  these  are  small  and  apparently  have  no  axones  (amacrine 
cells).  Their  longer  dendrites  pass  toward  the  periphery,  their 
shorter  dendrites  toward  the  olfactory  tract.  Larger  multipolar 
cells,  whose  axones  end  in  the  molecular  layer,  also  occur  in  the 
granular  layer. 

The  layer  of  longitudinal  fibre  bundles  consists  mainly  of  the 
centrally  directed  axones  of  the  mitral  and  brush  cells.     These  fibres 


44§ 


THE   ORGANS. 


run  in  distinct  bundles  separated  by  neuroglia.  Leaving  the  bulb 
they  form  the  olfactory  tract  by  means  of  which  they  pass  to  their 
cerebral  terminations. 

The  brush  cells  and  mitral  cells  with  their  processes  thus  consti- 
tute neurone  system  No.  II.  of  the  olfactory  conduction  path. 

TECHNIC. 

(i)  Carefully  remove  the  olfactory  portion  of  the  nasal  mucosa  (if  human 
material  is  not  available,  material  from  a  rabbit  is  quite  satisfactory).  This  may 
be  recognized  by  its  distinctly  brown  color.  Fix  in  Flemming's  fluid  (technic  7, 
p.  6).  or  in  Zenker's  (technic  9,  p.  6).  Stain  thin  vertical  sections  with  haematoxy- 
lin-eosin  (technic  1.  p.  16)  and  mount  in  balsam. 

(2)  For  the  study  of  the  nerve  relations  of  the  olfactory  cells  material  should 
be  treated  by  the  rapid  Golgi  method  (page  27). 


The  Organ  of  Taste. 

The  organ  of  taste  consists  of  the  so-called  taste  buds  of  the  lin- 
gual mucosae.  These  have  been  mentioned  in  connection  with  the 
papillae  of  the  tongue  (page  182)  and  under  sensory  end-organs  (page 

349)- 

The  taste  buds  are  found  in  the  side  walls  of  the  circumvallate 

papillae  (page  181),  of  some  few  of  the  fungiform  papillae,  in  the  mu- 
cosa of  the  posterior  surface  of  the  epi- 
glottis, and  especially  in  folds  (foliate 
papillae)  which  occur  along  the  postero- 
lateral margin  of  the  tongue. 

The  taste  bud  (Fig.  286)  is  an  ovoid 
epithelial  structure  embedded  in  the  epi- 
thelium and  connected  with  the  surface 
by  means  of  a  minute  canal,  the  gustatory 
canal  (Fig.  286,  a),  the  outer  and  inner 
ends  of  which  are  known  respectively  as 
the  outer  and  inner  taste  pores. 

Each  taste  bud  consists  of  two  kinds 
of  cells,  neuro-epithelial  cells  or  gustatory 
cells  and  sustentacular  cells  (Fig.  286). 
The  gustatory  cells  are  long,  delicate, 
spindle-shaped  cells  which  occupy  the 
centre  of  the  taste  bud,  each  ending  externally  in  a  cilium-like  proc- 
ess, which  usually  projects  through  the  inner  pore.     The  inner  end 


KIG.  286. —Taste-bud  from  Side 
Wall  of  Circumvallate  Papilla. 
•  Merkel-Menle.)  a,  Taste-pore  ; 
/',  nerve  fibres,  some  of  which  en- 
ter the  taste-bud — intragemin- 
al  fibres,  while  others  end  freely 
in  the  surrounding'  epithelium 
— intergeminal  fibres. 


THE   ORGANS   OF  SPECIAL   SENSE.  449 

of  the  cell  tapers  down  to  a  fine  process,  which  may  be  single  or 
branched.  The  sustentacular  cells  are  long,  slender  cells  which  form 
a  shell  several  cells  thick  around  the  gustatory  cells.  Sensory  termi- 
nals of  the  glosso-pharyngeal  nerves  (Fig.  286,  b)  end  within  the  taste 
buds  in  a  network  of  varicose  fibres — intrageminal  fibres.  Other  sen- 
sory terminals  of  the  same  nerve  end  freely  in  the  epithelium  between 
the  taste  buds.  These  are  finer  and  smoother  than  the  intrageminal 
fibres  and  are  known  as  intergeminal  fibres  (Fig.  286). 

TECHNIC 

(1)  The  general  structure  of  the  taste  buds  is  shown  in  the  sections  of  tongue 
(technic,  p.  182). 

(2)  For  the  study  of  the  nerve  terminals  the  method  of  (iolgi  should  be  used 
{page  27). 

General  References  for  Further  Study. 

Schwalbe  :  Lelirbuch  der  Ana  torn  ie  der  Sinnesorgane,  18S7. 
Kolliker  :  Handbuch  der  Gewebelehre  des  Menschen. 
Ramon  y  Cajal :   La  retine  des  vertebres.     La  Cellule,  ix.,  1893. 
McMurrich  :  The  Development  of  the  Human  Body. 
29 


IN  DEX. 


Absorption,  214 

of  fat,  216 
Accessory  olivary  nucleus,  374,  377,  380 
Achromatic  spindle,  40 
Acid  aniline  dyes,  15 
Acidophile  granules,  87 
Acini,  173 
Acoustic  stria?,  384 
Adrenal,  266 

blood-vessels  of.  26S 

development  of,  268 

nerves  of.  268 

structure  of,  266 

technic  of,  269 
Adventitia  of  arteries,  121 

of  lymph  vessels.  129 

of  veins,  124 
Afferent  peripheral  nerves,  338 
Agminated  follicles,  204 
Air-cells,  246 
Air-passages,  245 
Air-sacs,  246 
Air-vesicles,  245 
Alcohol,  as  a  fixative,  4 

dilute  as  a  fixative,  5 

-ether  celloidin,  9 

for  hardening,  7 

graded,  7 

Ranvier's,  4 

strong,  as  fixative,  5 
Alimentary  canal,  175 

development  of,  234 

endgut.  206 

foregut.  191 

headgut,  176 

midgut.  200 
Altmann's  granule  theory  of  protoplas- 
mic structure.  34 
Alum-carmine,  15 

for  staining  in  bulk.  17 
Alveolar  "lands.  17^; 


Amacrine  cells,  422 
Amitosis,  39 
Amoeboid  movement,  3S 
Amphophile  granules,  Sy 
Ampullae,  436 

of  Thoma,  146 
Anaphase.  41 
Aniline  dyes,  acid,  15 

basic,  15 
Anistrophic  line,  93 
Annular  terminations,  350 
Annuli  fibrosi,  126 
Anterior  horns,  342 

root  or  motor  cells  of.  352 

median  fissure.  341 

pyramids.  362,  376.    37S.   3S1.  3S5, 

3%  392 
Antero-lateral  ascending  tract.  361 
Antrum,  291 
Appendix  epididymidis,  279 

testis,  279 

vermiform  is.  20S 
Arachnoid  membrane,  334 

of  optic  nerve.  424 
Arbor  vita?.  397 
Arborescent  terminations.  350 
Archoplasm,  37 

Arciform  nucleus,  374.  377.  3S0.  3S1 
Arcuate  fibres,  external.  375.  377.  3S0, 

3's< 
internal.  374.  377,  37S.  3S1.  385. 

3S9 
Arrector  pili  muscle.  322 
Arterias  arciformes.  262 
Arteries.  1  r8 

adventitia  of.  121 

aorta  and  other  large.  121 

arcuate.  262 

arteriole.  1 19 

coats  of.  1  iS 

development  of,  128 


45' 


452 


INDEX. 


Arteries,  elastic  tissue  of.  121 

greater  arterial  circle  01  iris.  428 

hepatic.  229 

intima  of.  120 

large,  like  the  aorta.  121 

lesser  arterial  circle  of  iris.  428 

media  of.  12 1 

medium-sized.   119 

phrenic.  263 

precapillary  artery,  119 

recurrent.  263 

small.  119 

suprarenal.  263 

technic  of.  124 

vasa  vasorum  of,  124 
Arteriole.  1 19 
Articular  cartilages,  165 
Articulations.  165 

diarthrosis,  165 

synchondrosis,  165 

syndesmosis,  165 

technic  of.  166 
Association  fibres,  405 
Atresia  of  follicle,  296 
Atria.  246 

Attraction  sphere,  36 
Auditory  canal.  433 

hairs.  437 

pit.  444 
Auerbach's  plexus.  202,  213 
Auriculo-ventricular  ring.  126 
Axis  cylinder.  108,  350 
Axolemma  and  neurilemma,  relation  of, 

109 
Axone.  106 

development  of,  333 
hill.  ro6 

medullated,  109 
non-medullated,  107 

BAILLARGER,  inner  line  of.  402 

outer  line  0!.  402 
Balsam,  Canada,  for  mounting.  18 
Bartholin,  .udm'ds  (,f,  308 
Basal  granule,  59 
Basic  aniline  dyes.  15 
Basket  cells.  178 
Basophile  granules,  87 
Bertini,  <  olumns  of,  256 
Bethe,   concerning   continuity  of    axo- 
lemma  and  neurilemma.  109 


Betz,  cells  of.  404 
Bipolar  nerve  cells.  102 
Blastoderm,  46 
Blastomeres,  45 
Blocking,  9 
Blood.  85 

corpuscles,  SS 
crenation  of  red  cell,  86 
development  of,  88 
erythrocytes  of.  85 
haemoglobin  of,  85 
Jenner's  stain  for,  24 
leucocytes  of,  S6 
platelets,  88 
red  cells  of,  85 
smears,  technic  of,  90 
stroma  of,  85 
technic  of.  89 
vascular  unit,  249 
white  cells  of,  86 
Blood-islands,  88,  128 
Blood-vessel  system,  115 
arteries,  1 18 
capillaries,  1 17 
heart.  125 
lining  of,  1 17 
technic  of,  124,  127 
veins,  122 
Blood-vessels.  1 16 

lymph  channels  of,  124 
nerves  of.  124 
technic  of,  124 
Body  cavity,  129 
Bone  breakers.  159 

decalcification  of,  8 
formers.  157 
Bone  marrow.  152 
technic  of,  156 
red.  152 

cells  of.  152 

eosinophile  cells  of,  154 

fat  cells  of,  151 

mast  cells  of,  154 

multinuclear  cells  of,  133 

myelocytes  ol,  152 

myeloplaxes  ol.  153 

non  nucleated    red    blood    cells 

ol.   ,53 
nucleated    red    blood    cells   of, 

'53 

yellow.   154 


INDEX. 


A  r  1 

4  DO 


Bone  marrow,  yellow,  gelatinous,  154 
Bone  tissue,  82 

cells  of,  S3 

cementum,  1S6 

lacunas  and  canaliculi  of,  S3 

lamellae  of,  S3 

technic  of,  S3 
Bones,  14S 

blood-vessels  of.  155 

cancellous  or  spongy,  14S 

circumferential  lamellae  of,  151 

development  ofr  156 

growth  of,  163 

hard  or  compact,  14S 

Haversian  canals  of.  150 
lamellae  of,  150 

interstitial  lamellae  of,  151 

lymphatics  of.  155 

nerves  of.  155 

perforating  fibres,  152 
fibres  of  Sharpey,  152 

periosteum  of.  151 

technic  of.  156 

developing"  bone.  164 

Volkmann's  canals.  151 
Bony  spiral  lamina.  43S 
Borax-carmine,  alcoholic  solution.  17 
Bowman,  capsule  of.  256 

membrane  of.  413 
Brachia  conjunctiva.  393 
Brain,  see  Cerebrum 

membranes  of.  334 
arachnoid.  334 
dura  mater.  334 
pia  mater.  334 

relation  to  optic  nerve.  424 

sand.  41 1 
Bronchi.  242 

development  of,  250 

primary.  242 

respiratory.  245 

structure  of  walls  of.  242 

technic  of.  251 

terminal.  245 
Bruch,  membrane  of.  416 
Brunner"s  glands.  205 
Bulbus  oculi,  see  Eyeball 
Burdach.  column  of.  346.  3C 
Bursas.  16S 

Biitschli's  theory  of  protoplasm  struct- 
ure. 34 


Cajal,  cells  of.  403 
Cajeput  oil  for  clearing  sections,  iS 
Calcification  centre,  157 
Calcification  zone,  162 
Canaliculi  of  bone,  S3 
Canalis  communis,  436 
Canalized  fibrin,  306 
Cancellous  bone,  158 
Capillaries,  117 

chyle,  213 

development  of,  128 

technic  of,  124 
Capillary  network.  11S 
Capsule  of  Glisson,  227 
Carbol-xylol  for  clearing  specimens,  18 
Cardiac  glands,  196 
Carmine,  alum,  15 

borax,  7 

gelatin,  20 

neutral,  15 

picro-.  16 
Carotid  gland.  130 
Cartilage,  79 

cells.  79 

development  of,  82 

elastic.  Si 

fibrous.  Si 

hyaline.  So 

perichondrium,  82 

technic  of.  S2 
Cartilages,  the.  164 

articular.  164 

costal,  164 

skeletal,  164 

technic  of.  166 
Caryochromes.  104 
Cell.  the.  ^1 

body  of.  33 

centrosome  of.  ^ 

function  of.  37 

irritability  of.  37 

membrane  of.  ^ 

metabolism  of.  yi 

motion  of.  38 

nucleolus  of.  36 

nucleus  of.  33 

primary  germ  layers  of.  43 

reproduction  of,  39 

structure  of.  33 

technic  of.  46 

vital  properties  of.  37 


454 


INDEX. 


Cell-division,  direct.  39 

indirect.  39 
Cell  islands  of  Langerhans,  225 
Celloidin,  alcohol-ether.  9 

clove-oil.  10 

embedding",  9 
Cells,  acid.  215 

adelomorphous,  195 

air.  245 

amacrine.  422 

basket.  178.  399 

blood.  85 

bone.  S3 

brush.  447 

centro-acini.  of  Langerhans, 

centro-tubular.  223 

chief,  195.  410 

chromophile.  410 

colloid.  252 

compound  tactile,  34S 

decidual,  303 

Deiter's,  441 

delomorphous,  195 

eosinophile.  154 

epithelial.  53 

extrinsic,  346 

foetal,  248 

goblet,  201 

Golgi,  Type  I..  106 

Golgi,  Type  II.,  106,  404 

granule,  398 

gustatory.  448 

hair,  437.  441 

hecateromeric,  354 

Hensen"s,  441 . 

heteromeric,  354 

intrinsic,  346 

Kupffer's,  233 

Leydig's,  430 

lutein,  293 

marrow,  152 

mast.  65.  88.  154 

mesamceboid  cells.  52 

mitral,  447 

nerve.  346 

neuroepithelial,  437 

of  Claudius.  442 

oxyntic,  195 
Paneth's,  203 

parietal,  196 

peptic.  195 


Cells,  pillar,  441 

plasma,  64 

prickle,  314 

Purkinje,  397,  399 

replacing,  56 

respiratory,  247 

Sertoli,  272 

simple  tactile,  348 

spermatids,  274 

spermatocytes,  274 

spermatogenic,  272 

spermatogones,  273 

sustentacular,  224.  437 

tautomeric.  354 

wandering",  04,  202 
Cementing  glycerin  mounts.  18 
Cementum,  186 
Central  canal,  342 
Central  gelatinous  substance,  342,  343 

nervous  system,  see  Nervous  sys- 
tem {cerebro-spinal) 

tegmental  tract,  384,  387,  389 
Centro-acinar  cells  of  Langerhans,  223 
Centrosome,  33,  36 
Centrosphere,  36 
Cerebellar  peduncles,  391 
Cerebello-olivary  fibres,  377,  379 
Cerebellum,  397 

arbor  vita?,  397 

basket  cells  of,  399 

cortex  of,  397 

dentate  nucleus  of,  401 

general  histology  of,  397 

gray  matter  of,  397 

lamin;e  of,  397 

peduncles  of,  391,  402 

Purkinje  cells  of,  397 

teclinic  of,  407 
Cerebral  convolution,  402 

peduncles,  396 
Cerebro-spinal  ganglia,  336 

teclmic  ol,  338 
Cerebro-spinal     nervous     system,    sec 

Nervous  system  {cerebrospinal) 
Cerebrum,  402;  see  also  Cortex  cerebri 

convolutions  of,  402 

cortex  of,  402 

histology  of,  402 

technic  of.  407 
Ceruminous  glands,  433 
Cervix,  300 


INDEX. 


455 


Cervix,  technic  of,  310 
Chiasma,  optic,  426 

Chloride  of  gold  for  staining  connective- 
tissue  cells,  23 
Choriocapillaris,  415 
Chorion,  304 
Chorionic  villi,  305 
Choroid,  the,  415 

choriocapillaris  of,  415 

fissure,  432 

Haller's  layer  of,  415 

lamina  citrea,  416 

suprachoroidea,  415 

perichoroidal     lymph     spaces     of, 

plexus,  380,  38 1 

tape  turn  cellulosum  of,  415 
fibrosum  of,  415 

venae  vorticosa?  of,  415 

vitreous  membrane  of,  416 
Chromatin,  36 

Chrome-silver  method  of  Golgi,  23 
Chromophilic  bodies,  104 
Chromosomes,  40 
Chyle  vessels,  213 
Ciliary  artery,  427 

movement,  38 

plexus,  429 

processes,  417 
Ciliary  body,  the,  416 

blood-vessels  of,  428 

canal  of  Schlemm,  41S 

ligamentum  pectinatum,  418 

muscles  of,  41S 

pars  ciliaris  retinae,  417 

spaces  of  Fon tana,  418 
Circulatory  system,  115 

blood-vessel  system,  115 

development  of,  128 

lymph-vessel  system,  128 
Circumferential  lamellae,  151 
Circumvallate  papillae.  180 
Clarke's  columns,  344 
Claudius,  cells  of,  442 
Clearing  specimens  before  mounting,  18 
Clefts  of  Schmidt  Lantermann,  109 
Climbing  fibres,  400 
Clitoris.  30S 
Clouet*s  canal,  427 
Clove-oil  celloidin.  10 
Coccygeal  glands,  130 


Cochlea,  438 

bony  spiral  lamina  of,  43S 

cupola  of,  438 

hamulus  of,  43S 

helicotrema,  439 

membranous  spiral  ligament  of,  43S 

modiolus  of,  438 

scala  tympani,  439 
vestibuli,  439 

spiral  ligament  of,  438 
Cochlear  duct,  439 

basilar  membrane  of,  440 

crista  basillaris,  440 

external  spiral  sulcus.  440 

membrane  of  Reissner,  440 

organ  of  Corti,  441 

spiral  prominence  of,  440 

stria  vascularis,  440 

zona  pectinata,  441 
tecta,  441 
Coelum,  129 
Cohnheim's  field,  94 
Collaterals,  106 
Colloid,  251,  410 
Colostrum  corpuscles,  330 
Columnar  rectales,  210 
Columns  of  Bertini,  256 

of  spinal  cord,  342,  344,  346,  352,  353 
Commissural  fibres.  405 
Conduction  path,  358 
Cone  association  neurones.  425 
Cone  fibres.  421 
Cone-visual  cell,  421 
Cones,  layer  of  rods  and,  421 
Conjunctiva.  430 

end -bulbs  of,  349 
Connective  tissue.  63 

adipose  or  fat,  75 

areolar,  67 

bone,  82 

cartilage,  79 

cells,  64 

characteristics  of,  63 

chloride  of  gold  method  for  demon- 
strating cells  of,  23 

classification  of,  63 

elastic,  68 

embryonal,  71 

fibrillar,  64 

formed,  67 

histogenesis  of.  63 


456 


INDEX. 


Connective  tissue,  interalveolar,  248 

intercellular  substance  of,  65 

intrafascicular,  16S.  339 

lymphatic,  75 

loose,  67 

Mallory's  stain  for.  24 

mucous,  71 

neuroglia.  84 

periglandular,  327 

reticular,  j^ 

retinaculas  cutis,  313 

staining  cells  of,  23 

technic  for,  70,  73,  75,  79 

theories   of  development   of  fibres 
of.  68 
Constrictions  of  Ranvier,  109 
Corium.  see  Derma 
Cornea,  the,  412 

anterior  elastic  membrane  of,  413 

corneal  corpuscles  of,  414 

endothelium  of  Uescemet  of,  414 

epithelium  of,  412 

layers  of,  412 

membrane  of  Bowman  of,  414 
of  Descemet  of,  414 

perforating  or  arcuate  fibres  of.  414 

posterior  elastic  membrane  of,  414 

substantia  propria  of,  414 
Corneal  corpuscles,  414 
Cornua.  342 

Corona  radiata,  396,  405 
Corpora  amylacea,  283 

cavernosa,  284 

quailrigemina,  395 

anterior,  391,  395,  396 
posterior,  391,  395 
Corpus  albicans,  294 

callosum,  405 

haemorrhagicum,  293 

Highmori,    or   mediastinum    testis, 
270 

luteum,  293 

theory  of.  29 

spongiosum.  2S4 
Corpuscles,  blood.  .S5 

colostrum,  330 

crescentic,  383 

of  Grandry,  348 

Meissner,  349 

Merkel,  348 

Pacinian,  350 


Corpuscles,  Ruffini,  325 
Cortex   cerebelli,  397 ;    see   also    Cere- 
bellum 
Cortex  cerebri,  402  ;  see  also  Cerebrum 

association  fibres  of,  405 

barren  or  molecular  layer  of,  403 

cells  of  Betz,  404 

of  Golgi,  Type  II.,  404 
of  Martinotti,  404 

commissural  fibres,  405 

corona  radiata  of,  405 

deep  tangential  fibres  of.  404 

layer  of  polymorphous  cells.  403, 
405 
of  pyramidal  cells  of,  403 

projection  fibres,  405 

superficial  tangential  fibres  of,  403 
Cortical  pyramids,  256;  see  also  Kid- 
ney 
Corti's  arches,  442 

organ,  441 ;  see  also  Organ  of  Corti 

tunnel,  442 
Cotyledons,  305 
Cowper's  glands,  284 
Cox-Golgi  method  of  staining.  28 
Cranial  nerves,  368 ;  see  also  Nerves, 

cranial 
Crenation,  86 
Crescentic  corpuscles,  283 
Crescents  of  Gianuzzi,  178 
Crista  acustica,  438 

basillaris,  440 
Crura  cerebri,  396 
Crusta,  35,  3m 
Crypt  of  Lieberkiihn,  203 
Cumulus  oophorus,  291 
Cupola,  438 
Cupula,  438 

Cuticle,  see  Epidermis 
Cuticula.  35 
dentis,  186 
Cystic  duct,  233 
Cytoplasm,  34,  103 

Decalcifying,  8 

fluids,  8 
Decidua  basalis.  303 
capsularis,  303 
graviditatus,  303 
menstrualis,  302 
placentalis  subchorialis.  306 


INDEX. 


457 


Decidua  basalis,  reflexa,  303 
serotina,  303 
vera,  303 
Decolorizing  fluid  for  Weigert's  hema- 
toxylin, 26 
Decussation  of  fillet,  374,  377 

optic,  426 

of  pyramids,  371 

sensory,  374,  377 
Dehiscent  glands,  173 
Deiter's  cells,  441 

nucleus,  383 
Delafield's  haematoxylin,  14 
Demilunes  of  Heidenhain.  178 
Dendrites,  the.  106 
Dental  periosteum,  187 
Dental  sheath,  Neumann's,  185 
Dentate  nucleus,  401 
Dentinal  pulp,  183 
Dentine,  185 
Derma,  or  corium,  311 

corpuscles  of  Meissner,  349 

pars  papillaris,  312 
reticularis,  311 
Descemet,  endothelium  of.  414 

membrane  of,  414 
Deutoplasm,  35 
Development  of  teeth,  187 

common  dental  germ,  187 

cuticular  membrane,  189 

dental  papilla.  187 
ridge,  1S7 

enamel  organ,  1S7 

special  dental  germ,  187 

technic  of,  190 

Tomes'  process,  189 
Diapedesis,  88 
Diarthrosis,  165 
Diaster,  42 
Digestive  system.  175 

alimentary  tract  of,  175 

development  of,  234 

endgut,  206 

foregut.  191 

headgut,  176 

larger  glands  of,  217 

midgut,  200 

pancreas.  221 

the  gall-bladder.  233 

the  liver.  227 
Direct  cerebe'lar  tract.  361 


Discus  proligerus,  291 
Dissociation  of  tissue  elements.  4 
Dogiel's   theory  of  structure  of  spinal 

ganglion,  336 
Dorsal  accessory  olivary  nucleus,   378. 

380 
Dorso-lateral  ascending  tract,  361 

spino-cerebellar  fasciculus.  361 
Duct  systems  of  glands,  173 
Ducts,  aberrans  Halleri.  279 

Bartholini's,  219 

Bellini's,  257 

cochlear,  439 

common,  233 

excretory,  of  glands,  173 

cystic,  233 

ejaculatory,  278 

Gartner's,  296 

hepatic,  229 

Alullenan,  310 

nasal.  430 

oviduct,  297 

pancreatic,  222 

pronephritic,  309 

reuniens,  436 

Santorini's,  222 

secondary  pancreatic.  222 

seminal,  276 

utriculo-saccular,  436 

Wharton's,  219 

Wirsung's,  222 

Wolffian,  309 
Dura  mater,  334 

blood-vessels  of.  335 

technic  of,  335 
Dyes,  aniline,  15 

nuclear,  13 

plasma,  15 

Ear,  external,  433 
auricle,  433 
blood-vessels  of,  434 
ceruminous  glands  of.  433 
ear  drum ,  434 

external  auditory  canal.  433 
lymphatics  of.  434 
nerves  of.  434 
pinna,  433 

tympanic  membrane.  434 
internal,  435 

ampulla,  436 


458 


INDEX. 


Ear.  internal,  blood-vessels  of.  443 
canalis  communis.  436 
cochlea.  438 
duct.  439 

endolymph  of.  435 
fenestra  ovalis.  435 
lymphatics  of.  443 
membrana  tectoria.  443 
membranous  labyrinth.  435.  436 
nerves  of,  443 
organ  of  Corti.  441 
osseous  labyrinth  of,  435 
perilymph  of.  435 
saccule.  437 

semicircular  canals,  436 
utricle.  437 
vestibule.  435 
middle,  or  tympanum.  434 
fenestra  rotunda  of,  435 
ossicles  of,  435 
Ear  drum.  434 

wax.  433 
Ebner's  glands,  1S2 

hydrochloric-salt  solution,  8 
Ectoderm.  45 

tissue,  derivations  from,  51 
Efferent  peripheral  nerves,  338 
Egg  nest.  290 
Ejaculatory  ducts.  278 
Elastic  cartilage.  81 
tissue.  68 

Weigert's  stain  for,  23 
Eleidin.  314 

Ellipsoid  of  Krause.  421 
Ellipsoids  of  spleen,  144 
Embedding.  9 
celloidin.  9 
paraffin,  1 1 
Embryonal  tissue,  7; 
Enamel.  [86 
fibres.  186 
organ,  187 
prisms.  186 

lines  of  Retzius  of.  186 
End-bulbs,  349 

of  Krause.  182.  326 
Endgut,  206 

large  intestine.  206 
rectum.  210 

\  ermiform  appendix,  208 
Endocardium,  126 


Endochondral  ossification,  159 
Endolymph,  433 
Endolymphatic  sac,  436 
Endomysium.  16S 
Endoneurium,  339 
Endoplasm,  35 
Endothelial  tube,  12S 
Endothelium.  60 
Entoderm,  46 

tissue  derivations  from,  51 
Eosin,  15 

Eosinophile  granules,  87 
Ependymal  cells,  333 
Epiblast.  45 
Epicardium,  127 
Epicranium,  158 
Epidermis  (or  cuticle),  313 

stratum  corneum  of,  314 
cylindricum  of,  313 
germinativum  of,  313 
granulosum  of,  314 
lucidum  of,  314 
Malpighii  of,  313 
mucosum  of.  313 
spinosum  of,  314 
Epididymis,  271 
Epidural  space.  334 
Epimysium,  167 
Epineurium.  339 
Epiphyseal  cartilage,  164 
Epithelium,  53 

cells  of,  53 

ciliated,  59 

classification  of,  54 

cuboidal,  55 

general  characteristics  of,  53 

germinal,  288 

glandular,  60 

histogenesis  of,  53 

intercellular  bridges  of.  53 

lens,  426 

membrana  propria  of,  53 

neuro-,  60 

pigmented,  60 

pseudo-stratified,  56 

respiratory,  247 

simple,  54 

columnar,  54 
pseudo-stratified,  56 
squamous,  54 

stratified.  56 


INDEX. 


459 


Epithelium,  stratified,  columnar.  58 
squamous.  56 
transitional,  57 

surface,  of  mucous  membranes,  174 

syncytium.  305 

technic  of,  61 

transitional,  57 
Eponychium,  318 
Epoophoron,  296 
Erectile  tissue,  285 
Erythroblasts,  153 
Erythrocytes,  85 
Erythrosin.  15 
Eustachian  tube,  435 
Exoplasm,  35 
External   arcuate  fibres.   375,  377,  380, 

381 

External  ear.  see  Ear,  external 
Eyeball  (or  bulbus  oculi),  412 

blood-vessels  of,  427 

choroid  of.  415 

ciliary  body  of,  416 

cornea  of,  412 

iris  of.  418 

lymphatics  of,  428 

nerves  of.  429 

retina  of,  420 

sclera  of.  412 

technic  of,  432 
Eyelid,  the.  430 

blood-vessels  of.  430 

conjunctiva  of,  430 

epidermis  of.  430 

glands  of,  430 
of  Mall,  430 

lymphatics  of,  431 

Meibomian  glands,  430 

muscles  of,  430 

nerves  of,  431 

tarsus  of,  430 

technic  of.  433 

Fallopian  tube,  see  Oviduct 
Fascicles  of  muscle,  167 

of  nerves.  339 
Fasciculus,  posterior  longitudinal,  375, 
377.  3S0.  381.  386 
solitarius,.374.  377.  3S0 
ventrolateralis  superhcialis,  361 
Fat,  absorption  of,  214 
technic  of.  217 


Fat.  osmic-acid  stain  for,  24 
secretion,  214 
subcutaneous,  313 
tissue,  75 
Female  genital  organs,  288 
Fenestra  ovalis,  435 

rotunda,  435 
Fertilization  of  the  ovum,  42 
Fibre  baskets,  423 
systems,  358 

short,  364 
tracts  of  spinal  cord,  358 

of  spinal  cord,  technic  of,  366 
Fibre  tracts  of  spinal  cord  (ascending), 
360 
anterolateral  ascending   tract. 

361 
direct  cerebellar  tract.  361 
dorsolateral    ascending    tract, 

36i 

dorso-lateral      spino  cerebellar 
fasciculus,  361 

fasciculus     ventrolateralis     su- 
perficialis,  361 

Gowers'  tract,  361 

posterior  columns,  360 

tract  of  Flechsig,  361 
(descending),  362 

anterior    marginal     bundle    of 
Loewenthal,  363 

antero-lateral  descending",  363 

comma  tract  of  Schultze,  364 

crossed  pyramidal  tract.  362 

direct  pyramidal  tract,  362 

Hehveg's,  363 

oval  bundle  of  Flechsig.  363 

pyramidal  tracts,  362 

rubro-spinal,  363 

septo-marginal,  363 

tract  of  Tiirck,  362 

Von  Monakow's  tract.  363 
Fibres,  449 

calcined.  157 

cone.  421 

dentinal.  184 

development   of    connective-tissue, 

6S 
enamel.  186 
genioglossal,  179 
intergeminal.  449 
intrageminal.  448 


460 


INDEX. 


Fibres,  lens,  426 

Mallory's  method  of  staining  con- 
nective tissue,  24 
mantle.  40 
Miiller's.  422 
nerve,  see  also  Nerve  fibres 

medulla  ted.  10S 

non-medulla  ted.  107 
neuroglia.  1 12 
of  areolar  tissue.  67 
of  bone.  S3 

of  developing  muscle,  99 
of  formed  connective  tissue,  67 
of  Remak,  108 
of  Sharpey,  152 
olfactory,  layer  of.  447 
perforating  or  arcuate,  of   cornea. 

4H 
of  Sharpey.  152 
picro-acid-fuchsin  for  staining  con- 
nective-tissue, 16 
rod,  421 
tendon,  67,  168 
tunnel.  444 

voluntary  muscle.  92.  95 
Weigert's  method  for  staining  elas- 
tic. 23 
method  for  staining  nerve.  25 
white  or  fibrillated,  65 
yellow  or  elastic.  65.  68 
Fibrillar  connective  tissue.  64 

theory  of  protoplasm  structure,  34 
Fibroblasts,  68 
Fibrous  cartilage,  81 
Filiform  papilla1.  1S0 
Fillet,  the.  374.  377,  379,  381,  3S5,  389, 

393 
Filum  term  in  ale,  340 
Fissure,  anterior  median.  41 

choroid.  432 
Fixation,  4 

by  injection,  5 

in  to  to,  5 
i  ixatives,  5 
Flechsig,  oral  bundle  of,  363 

tract  of.  361 
1- "le. nming's  fluid,  6 
.  oam   theory  of  protoplasm  structure, 

34 
1  oiiate  papilla?,  448 
Follicle,  ( Graafian,  289 


Follicular  cavity  or  antrum.  291 
Folliculi  linguales,  see  Tonsils 
Foil  tana,  spaces  of.  418 
Foramina  nervosa.  444 
Forebrain.  332 
Foregut,  the.  191 

general    structure  of   walls   of   the 
gastro- intestinal  canal.  192 

oesophagus.  191 

stomach.  194 
Forel.  decussation  of,  394 
Formalin,  as  a  fixative,  5 

for  macerating.  4 
Formalin-M idler's  fluid,  5 
Fossa  navicularis.  287 
Fovea  centralis.  423 
Fuchsin.  1 5 
Function  of  cells,  37 
Fundamental   columns   of  spinal  cord, 

364 
Fungiform  papilla;,  1S0 
Funiculus  teres,  nucleus  of,  3S1 

Gage's  hematoxylin,  13 
Gall-bladder,  233 
Ganglia,  335 

Gasserian,  389 

spinal.  336 

spiral,  444 

sympathetic,  337 
Ganglion  cells,  336 
Gasserian  ganglion,  389 
Gastric  glands.  194 

Gastro-ihtestinal    canal,  general  struct- 
ure of  the  walls  of,  192 
Gelatin,  carmine  for  injecting.  20 

Prussian -blue,  for  injecting.  20 
Gelatinous  marrow.  154 

substance  of  Rolando,  342,  343 
Genioglossal  fibres,  179 
( renital  ridge.  310 
Gentian  violet,  15 
Genu  or  bend,  396 
(ierm  hill,  291 
Germinal  spot,  292 

vesicle.  42 
Gianuzzi,  crescents  of,  17S,  240 
<  riraldes,  organ  ol .  278 
Gland  cells,  170 
Glands,  170 

acini  of,  173 


INDEX. 


461 


Glands,  adrenal,  266 
alveolar.  173 

compound,  173 

simple.  173 
alveoli  of,  173 
axillary.  330 
Bartholini's,  30S 
Brunner's,  205 
cardiac.  196 
carotid.  130 
cells  of.  170 
ceruminous,  433 
classification  of,  171 
coccygeal.  130 
compound.  17  1 
Co\vper*s,  2S4 
epithelium  of.  1 70 
excretory  ducts  of,  17.-- 
dehiscent,  173 
ductless,  173 
Ebner's,  1S2 
gastric,  195 
haemolymph.  135 
internal  secreting.  173 
intraepithelial,  276 
lacrymal.  429 
Lieberkuhn's,  203 
lingual.  17S 
Littre  s.  2S7 
liver.  227 
lobes  of,  171 
lymph,  131 
Mall's.  430.  433 
mammary.  327 
Meibomian.  430 
mixed.  177 
mucous.  177 
of  the  oral  mucosa,  177 
pancreas.  221 
parathyroids,  252 
parenchyma  of,  171 
parotid.  218 
peptic.  195 
pineal.  41 1 
prostate.  2S2 
pyloric.  197 
reticular.  173 
saccular,  171 
salivary,  2  17 
sebaceous.  315.  323 
secreting  portions  of.  170 


Glands,  serous,  177 

simple.  171 

spleen,  142 

sublingual.  219 

submaxillary,  219 

sweat.  315 

tarsal.  430 

thymus,  138 

thyroid,  251 

tonsils,  140 

tubular,  171 

compound.  173 
simple  branched.  172 
simple  coiled.  172 
simple  straight,  172 

Tyson's,  286 
Glandulae  sudoriparae.  315 

vestibulares  majores.  308 
minous,  308 
Glandular  epithelium.  170 
Glans  penis,  2S6 
Glenoid  ligaments,  165 
Glisson.  capsule  of,  227 
Globus  major,  271 

minor,  271 
Glomerulis.  of  kidney,  256 

olfactory,  447 
Glycerin  for  mounting  specimens,  17 
Glycogen  granules.  231 
Golgi  bichlorid  method  for  nerve  tissue, 

27 
cell.  Type  I..  106 
cell,  Type  II.,  106,  404 
method,  bichloride,  27 
Cox  modification.  28 
formalin  bichromate.  27 
mixed,  27 

muscle-tendon  organs  of,  350 
net,  1 1 1 
rapid,  27 
silver.  27 

silver,  for  nerve  tissue.  27 
Golgi's  chrome-silver  method  of  stain- 
ing, 23 
Golgi-Mazzoni  corpuscles.  325 
Goll,  column  of,  346,  360 
Gowers' tract,  361.  370.  376.  378,  381, 

3S4,  3S9.  393.  394 
Graafian  follicles.  289 
antrum  of,  291 
germ  hill  of.  291 


462 


IXBEX. 


Graafian  follicles,  liquor  folliculi,  291 

ovum  of.  292 

rupture  of,  293 

technic  of,  299 

theca  folliculae  of,  291 
Graded  alcohols.  7 
Grandry.  corpuscles  of.  34S 
Greek  letter  granules  of  Ehrlich.  87 
Ground  bundles  of  spinal  cord,  364 
Gustatory  canal.  44S 

H.EMALU.M,  Mayer's.  14 
Haematin.  14 

Haematoidin,  crystals  of,  294 
Ha-matoxylin,  13 

and    eosin,    for     staining     double, 
16 

and  picro-acid  fuchsin,  16 

Delafield"s,  14 

Gage's.  13 

Heidenhain's,  14 

Mallory's  stain,  24 

Weigert*s.  2? 
Haemoglobin,  S5 
Hamolymph  nodes.  135 

blood  sinuses  ot.  135 

blood-vessels  of.  137 

cells  of,  136 

marrow-lymph,  136 

splenolymph.  136 

technic  of.  137 
Hair.  318 

arrector  pili  muscle  of  the,  322 

bulb,  318 

cells  ol  the.  319.  437 

cortex  of.  319 

cortical  fibres  of  the.  319 

cuticle  of.  319.  320 

cuticle,  Henle's  layer  of.  320 
1 1  uxley's  layer  of.  320 
root  sheath  of,  320 
the  prickle  cells  of.  320 

development  of  the.  y<> 

eyelashes,  430 

follicle.  319 
germ,  324 
growth  of  the.  324 
lanugo,  the.  319 

layers  of  the.  319,  320 
medulla  of.  319 
papilla  of.  318 


Hair,  root  of  the.  321 

sebaceous  glands  ol'  the.  322 

sebum  of  the,  323 

shaft  of,  31S 

shedding  of  the.  2>23 

technic  of  the.  324 
Haller's  layer,  415 
Hamulus,  438 
Hardening.  7 

celloidin-embedded  specimens.  9 

clove-oil  celloidin-embedded  speci- 
mens, to 
HassaTs  corpuscles,  139 
Haversian  canals,  150 

fringes.  166 

lamellae,  150 

spaces,  162 
Headgut,  176 

the  mouth.  176 

the  pharynx.  190 

the  teeth,  183 

the  tongue,  179 
Hearing,  organ  of,  433 
Heart,  125 

annuli  fibrosi.  126 

auriculo-ventricular  tint;'  of.  126 

blood-vessels  of.  127 

development  of,  128 

endocardium  of.  126 

epicardium  of.  126 

lymphatics  of.  127 

muscle,  96 ;    see  Involuntary  stri- 
ated muscle 

myocardium  of,  126 

nerves  of.  127,  350 

technic  of,  127 

valves  of.  127 
Hecateromeres.  354 
I  leidenhain.  demilunes  of,  178 
Heidenhain's  heematoxylin,    4 
I  leisterian  valve.  233 
1  lelicotrema,  439 
1  lelweg.  tract  of,  }<>;-, 
I  lenle's  layer,  320 

loop,  256 
I  [enle,  sheath  of,  339 
I  [ensen's  cells,  44  1 

line,  93 
1  [epatic  artery.  229 

cells,  230 

cords,  232 


INDEX. 


46; 


Hepatic  duct.  229,  233 
Heteromeres,  354 
Hindbrain,  332 
His,  marginal  veil  of,  333 

spongioblasts  of,  333 
Howship's  lacunae,  159 
Huxley's  layer.  320 
Hyaline  cartilage,  80 
Hyaloid  canal.  427 

membrane,  427 
Hyaloplasm.  34 
Hydatid  of  Morgagni.  310 
Hydrochloric  acid  for  decalcifying,  8 
Hyoglossal  fibres.  179 
Hypoblast,  46 
Hyponychium.  318 

Hypophysis  cerebri.  410 ;  see  also  Pitu- 
itary body 

Implantation  cone.  106 
Incisures  of  Schmidt-Lanterman.  109 
Inferior  brachium  quadrigeminum.  396 
cerebellar  peduncle,  see  Restiform 

body 
Injecting,  20 

apparatus,  21 
double.  22 
separate  organs. 21 
whole  animals,  21 
Inner  bulb,  350 
Innervation  of  muscles.  353 
Intercellular  bridges  of  epithelium.  53 
substance.  12 

of  connective  tissue,  fibres  of,  65 
silver-nitrate  method  of  stain- 
ing. 23 
Intermediate  lamella?,  151 
Internal   arcuate   fibres,    374,  377.  37S, 

381,  385, 3S9 
Internode,  109 
Interstitial  lamellae.  151 
Intestine,  see  Small  intestine  and  Large 

intestine 
Intestines,  development  of.  235 
Intima,  120 

of  arteries.  120 
of  lymph  vessels.  129 
of  veins.  123 
Intracartilaginous  ossification.  159 
Intrafascicular   connective    tissue.    168, 
339 


Intramembranous  ossification.  157 
Intranuclear  network  of  typical  cell.  36 
Involuntary  striated  muscle  (heart  mus- 
cle). 96 
Cohnheim's  field.  97 
McCallum's  views,  96 
membrane  of  Krause.  97 
muscle  columns  of  Kolliker.  97 
nerves  of,  350 
sarcoplasm  of.  97 
technic  of.  100 
smooth  muscle.  91 

intercellular  bridges  of.  92 
Iodine  to  remove  mercury.  7 
Iris,  the,  418 

greater  arterial  circle.  42S 
layers  of  the.  418 
lesser  arterial  circle.  428 
muscles  of  the.  419 
Irritability  of  cells.  37 
Islands,  blood.  8S.  128 
of  Langerhans.  225 
Isolated  smooth  muscle  cells.  91 

technic  of.  99 
Isotrophic  line.  93 

Jexxer's  blood  staix.  24 
Joint  capsule.  165 
Joints,  165 

Karyokixesis.  39 
Karyolysis.  314 
Karyoplasm.  36 
Karyosomes.  36 
Keratin,  314 

Keratohyaline  granules.  314 
Kidney,  the.  254 

blood-vessels  of.  261 

Bowman's  capsule.  256 

columns  of  Bertini.  256 

convoluted  tubules  of.  259 

cortex  of.  254 

cortical  pvramids  or  labyrinths  of. 

duct  of  Bellini.  257 

glomerulus  of.  256 

Henle's  loop.  259 

hilum  of.  254 

lobulated.  254 

lymphatics  of.  264 

main  excretory  duct  of.  264 


4<H 


INDEX. 


Kidney,  Malpighian  body.  25S 
medulla  of.  254 
medullary  or  Malpighian  pyramid. 

-56 
rays,  or  pyramids  of  Ferrein, 
'256 

nerves  of.  264 

pelvis  of.  255 

renal  corpuscle,  256 

renculi  or  lobes  of  the,  254 

septa  renis,  256 

technic  of,  269 

urmiferous  tubule,  256 
Kidney-pelvis.  264 

calyces  of,  264 
Kolliker,  muscle-columns  of,  94 
Krause,  ellipsoid  of.  421 
Krause's  end-bulbs,  182.  326 

line,  93 
Kupffer.  cells  of,  233 

Labyrinth,  membranous,  435 

osseous,  435 
Lacrymal    apparatus,    lacrymal    canal, 
429 
lacrymal  gland,  429 
lacrymal  sac,  429 
nasal  duct,  430 
gland,  429 

blood-vessels  of,  430 
,    excretory  ducts  of,  429 
lymphatics  of,  430 
nerves  of,  430 
Lacunae,  79,  83 
Lamellse,  circumferential,  151 
Haversian,  150 
intermediate,  151 
interstitial,  j 5 1 
Lamina,  bony  spiral,  438 
citrea,  416 
cribrosa,  412,  424 
fusca.  412 

membranous  spiral,  438,  440 
reticularis,  443 
suprachoroidea,  415 
Lamina-  of  cerebellum,  397 
Langerhans,  cell  islands  of,  225 
centro-acinar  cells  of,  223 
centro-tubular  cells  of,  223 
Large  intestine.  206 

Auerbach's  plexus,  207 


Large  intestine,  coats  of,  206 

gland  tubules  of.  207 

lineae  coli,  207 

plexus  of  Meissner,  207 

technic  of,  216 
Larynx,  the,  239 

technic  of,  242 
Lateral  lemniscus,  3S7,  389,  393 
Lemniscus,  374,  387 
Lens,  426 

canal  of  Petit,  427 

capsule  of,  426 

epithelium  of,  426 

hyaloid  membrane,  427 

suspensory  ligament  of,  426 

zonula  ciliaris.  426 

zonule  of  Zinn,  426 
Leucocytes,  86 

of  milk,  330 
Lieberkuhn,  crypts  of,  203 

glands  of,  203 
Ligament,  membranous  spiral,  438 

spiral,  the,  438 

structure  of,  68 

suspensory,  426 
Ligamentum  pectinatum,  418 
Lineae  coli,  207 
Lines  of  Retzius,  186 
Lingual  glands,  178 
Lingual  tonsils,  141 
Lingualis,  genio-glossus  fibres  of,  179 

hyoglossus  fibres  of,  179 

longitudinal  fibres  of,  179 

styloglossus  fibres  of,  179 

transverse  fibres  of,    179 
Lin  in,  36 

Liquor  folliculi,  291 
Lissauer,  zone  of,  343 
Littre",  glands  of,  287 
Liver,  the,  227 

blood  supply  of,  229 

capsule  of  Glisson,  227 

connective  tissue  of,  227 

cells  of,  230 

of  Kupffer,  233 

development  of,  235 

glycogen  granules  of,  231 

hepatic  duct  of,  229 

lobule  of,  228 

lymphatics  of,  233 

main  ducts  of,  233 


INDEX. 


465 


Liver,  nerves  of,  233 
portal  canal  of,  230 
technic  of,  235 
Loewenthal,  anterior  marginal  bundle 

of.  363 
Lungs,  the.  244 
air  sacs  of,  246 

vesicles  of,  245 
alveolar  ducts  of,  245 
atria  of,  246 
blood-vessels  of,  249 
cells  of,  247 
epithelium  of,  247 
infundibula  of,  245 
interalveolar   connective   tissue  of, 

24S 
lymphatics  of,  250 
Miller's  subdivisions,  245 
nerves  of,  250 
pulmonary  pleura  of,  244 
respiratory  epithelium  of,  247 
technic  of,  251 
terminal  bronchi  of,  245 
Lunula.  318 
Lutein  cells,  293 
Luteum,  corpus,  293 
Lymph  capillaries,  129 

glands,  see  Lymph  nodes 
nodes,  131 

blood-vessels  of,  134 

capsule  of.  131 

connective  tissue  of,  131 

cords  of,  132 

cortex  of,  132 

germinal  centre  of,  132 

lymphatics  of,  134 

medulla  of,  132 

nerves  of,  134 

nodules  of,  132 

reticular  connective  tissue  of, 

sinuses  of,  132 

technic  of,  135 
nodule,  132 

germinal  centre  of,  132 
paths  of  the  eye,  42S 
spaces,  129 

pericellular,  129 
vessel  system,  128 

development  of,  129 

lymph  capillaries,  129 
30 


Lymph  capillaries,  vessel  system,  lymph 
spaces,  129 
technic  of,  129 
vessels,  coats  of,  129 
structure  of,  12S 
Lymphatic  organs,  131 

hasmolymph  nodes,  135 

lymph  nodes,    131 

spleen,  142 

technic  for,  134,  137,   139,   142, 

146 
thymus,  138 
tonsils,  140 
tissue,  75 
Lymphocytes,  86 
Lymphoid  tissue,  133 

Macerating  fluids,  4 
Maceration,  4 
Macula  acustica,  437 

lutea,  423 

fovea  centralis,  423 
Male  genital  organs,  270 
Mall,  glands  of,  430,  433 
Mallory's  haematoxylin  stain,  24 
Malpighian  bodies,  142 

body,  development  of,  258 

pyramid,  see  Kidney 
Mammary  gland,  327 

active,  32S 

alveoli  of  active,  328 

blood-vessels  of,  330 

cells  of,  329 

development  of,  331 

ducts   of,  327 

of  nipple.  327 

inactive,  32S 

lymphatics  of,  330 

nerves  of,  330 

secretion  of,  329 

structure  of,  327 

technic  of,  331 
Mantle  fibres,  40 
Marchi's  solution,  366 
Marginal  veil  of  His,  333 
Marrow,  see  Bone  /narrow 
Martinotti,  cells  of,  404 
Mast  cells,  88 
Maturation.  42 

McCallum.    concerning    heart    muscle. 
96 


466 


INDEX. 


.Media,  of  arteries.  121 

of  lymph  vessels.  129 

of  veins.  123 
Median  lemniscus,  die.  574.  377.  379,  3S5 

raphe.  377 

septum,  posterior.  341 
Mediastinum  testis.  270 
Medulla  oblongata.  367 

accessory  olivary  nucleus   of.   374. 

377-  3S° 
acousticae  striae.  3S4 
anterior  column  of.  370.  376 

ground  bundles  of.  370 

horns  of.  370.  376 

pyramid   of.   376.  37S.  3S1.  3S5, 

389 

arciform  nucleus  of.  374.  377,  3S0, 

381 

ascending  tracts  of,  36S 
central  canal  of.  371,  376 

gelatinous  substance  of,  371 

gray  matter  of.  377 

tegmental  tract.  384.  3S7,  389 
cerebellar  peduncles  of.  391 
cerebello-olivary  fibres.  377.  379 
choroid  plexus,  380.  381 
column  of  Burdach.  370.  371 

of  Goll.  370.  371 
compared  with  spinal  cord,  368 
crossed  pyramidal  tract.  370 
cranial  nerves  of.  368 
decussation  of  fillet.  374 

of  pyramids  of.  371 
descending  or  spinal  root  of  vestibu- 
lar portion  of  eighth  nerve, 
380 

tracts  of,  368 
direct  cerebellar  tract,  370.  376 
dorsal    accessory    olivary    nucleus, 
378,  380 

nucleus  of  ninth   cranial  nerve, 
378.  3S0 

nucleus  of  ten tli  nerve.  378.  380 

root  of  first  cervical!   nerve.  371 
external  arcuate  fibres  of.  -575.  377, 
380.  38, 

fiHet  of^  374-  377-  379-  3's'-  3S5-  389 
fourth    ventricle  of.    378.    }8o,    $86, 

389 

funiculus  cimea'iis.  370 
gracilis.  370 


Medulla  oblongata,  gelatinous  substance 

of  Rolando,  371 
general  structure  of,  367 
internal  arcuate  fibres  of,  374,  377, 

378.  381.  385,  3S9 
lateral  column.   370.   371.  376.   37S. 

38i 

lemniscus,  387.  389 
median  lemniscus.  374.  377.  371) 

raphe  of,  377 
nuclei  of  posterior  columns,  377 
nucleus  ambiguus,  37S.  380 
cuneatus.  373 
gracilis.  373 

of  the  column  of  Burdach,  373 
of  the  column  of  Goll.  373 
of  funiculus  teres.  381 
of    origin   of    eleventh    cranial 

nerve,  374 
of    origin    of    twellth     cranial 
nerve.  374.  377.  380 
olivary  nucleus.  375.  377.  380.  38] 
pons  Varolii,  386.  389 
posterior  columns  of.  370.  371.  376 
horns  of.  370.  376.  378.  381,  385 
longitudinal     fasciculus,      375, 
377.  380.  381.  386.  389 
restiform  body  of .  375.  377.  380,  3S1 
reticular  formation  of.  371,  377,  378, 

381,  389 

root  fibres  and  nucleus  of  origin  of 

sixth  cranial  nerve.  384.  386 

fibres  and  nucleus  of  origin  of 

seventh  cranial  nerve.  384.  386 

fibres     and     nuclei     of     eighth 

nerve,  382.  386 
fibres  of  ninth  and  tenth  cranial 

nerves,  378.  380 
fibres  of  eleventh  cranial  nerves, 

374 
fibres    of    the    twelfth     cranial 
nerve.  377 
section  through  decussation  of  fillet, 

37 ' 
through    exit  of  eighth    nerve. 

38l 
through  exit  of  root  fibres  of 

fifth  cranial  nerve,  388 
through  exits  of  root  fibres  of 

sixth     and     seventh     cranial 

nerves.  384 


INDEX, 


467 


Medulla     oblongata,     section     through 
lower  part  of  olivary  nucleus, 

37<5 
through  middle  of  olivary  nu- 
cleus, 378 
through  pyramidal  decussation, 
370 
sensory  decussation  of,  374 

and    motor   root   fibres   of   the 
fifth  nerve,  389 
solitary  fasciculus,  374,  377,  380 
spinal  (descending)  root  of  fifth  cra- 
nial nerve,  374,  377,  380,  381,  386, 

389 

sulco-marginal  tract  of,  370 
superior  olive  of,  387,  3S9 
technic  of,  396 
tract  of  Gowers,  370,  376,  37S,  381, 

384-  389 
of  Helweg,  370 

transverse  fibres  of  pons  Varolii,  3S4 

Von  Monakow's  bundle,   370,  376, 
37S,  381,  384,  3S9 
Medullary  rays,  256 
Medullary  sheath,  109 

vellum,  anterior,  391 
Medullated  nerve  fibres,  Weigert's  stain 

for,  25 
Meibomian  glands,  430 
Meissner,  corpuscles  of,  349 
Meissner's  plexus,  205,  214 
Membrana  propria,  53 
Membrana  tectoria,  443 
Membrane  of  Bowman,  413 

of  Descemet,  414 

of  Krause,  93,  97 

of  Re  issuer,  440 
Membranous  cochlea,  439 

spiral  lamina,  438,  440 
ligament.  438 
Meninges,  334 

Mercuric  chloride  as  a  fixative,  6 
Merkel's  corpuscles.  348 
Mesamoeboid  cells.  52 
Mesencephalic  root  of  fifth  (trigeminus) 

cranial  nerve,  391,  393 
Mesencephalon,  332 
Mesenchyme,  52 
Mesoblast,  46 
Mesoderm,  46 

tissue  derivatives  from,  52 


Mesonephros,  309 
Mesothelium,  52,  60 
Metabolism  of  cells,  37 
Metanephros,  309 
Metaphase.  41 
Metaplasm.  35 

Method  of  embryology  for  studying  fibre 
tracts  of  cord.  359 

of     pathology    for     studying   fibre 
tracts  of  cord,  359 
M ethyl  blue,  15 

green,  15 

violet,  15 
Meynert,  decussation  of,  394,  396 
Micron,  12 
Midbrain,  332 

anterior  corpora  quadrigemina  of, 

39 1 ,  395.396 
brachia  conjunctiva  of,  393 
crusta  of,  392,  394 
fillet  of,  393.  395 
fourth  cranial  nerve,  393 
geniculate  bodies  of,  395 
Cowers'  tract  of,  393,  394 
inferior  brachium  quadrigeminum, 

396 
lateral  lemniscus  of,  393,  395 
mesencephalic  root  of  fifth  nerve,  393 
posterior  corpora  quadrigemina  of, 

39 1 ,  395 
longitudinal  fasciculus,  393,  395 
pyramid  of,  392 
red  nucleus  of,  395 
reticular  formation  of,  393,  395 
section  through  exit  of  fourth  nerve, 

39i 
through  exit  of  third  nerve,  394 
superior    cerebellar    peduncles   of, 

393'  395 

tegmentum  of.  391.  393 

Von  Monakow's  bundle  of.  393 
Middle  ear,  see  FJar,  middle 
Midgut,  200 

small  intestine,  200 
Milk.  329   _ 

cells  of,  330 

colostrum  corpuscles  of,  330 
Miller's  theory  of  lung  subdivisions.  245 
Mitosis.  39 

method  of  demonstrating  by  Flem- 
ming's  fluid.  6 


468 


INDEX. 


Modiolus.  43S 
Monaster.  43 

Mononuclear  leucocytes.  86 
Motion  of  cells.  3S 
Motor  end-plate.  353 

peripheral  nerves,  338 
Mounting.  17 

celloidin  specimens.  iS 

in  balsam.  18 

in  glycerin.  17 

paraffin  sections.  19 
Mouth,  the,  176 

blood-vessels  of,  178 

end-bulbs  in  mucous  membrane,  349 

glands  of,  177 

lymphatics  of,  17S 

mucous  membrane  of,  176 

nerves  of,  178,  349 

technic  of,  179 
Mucous  glands.  177 

Mucous    membranes,   basement    mem- 
brane of.  174 

general  structure  of,  174 

muscular  is  mucosae  of,  174 

stroma  of.  174 

submucosa  of.  174 

surface  epithelium,  174 

tunica  propria  of,  174 
Mucous  tissue,  71 
Miiller.  circular  muscle  of,  41S 
Miiller's  fibres,  422 

fluid,  s 
Miiller ian  ducts,  310 
Multipolar  nerve  cells,  102 
Muscle,  arrector  pili,  322 

Ciliary,  418 

circular,  of  Miiller,  41S 

columns  of  Kolliker,  94 

discs.  93 

spindles  or  neuromuscular  bundles, 

Muscle-tendon  junction,  peripheral 
nerve  terminations,  350 
organs  of   Golgi,  peripheral  nerve 

terminations  in,  350 
Muscle  tissue,  91 

development  of,  98 

heart,  96 

involuntary  smooth,  91 

involuntary  striated,  96 

technic  of,  99 


Muscle  tissue,  voluntary,  striated,  92 
voluntary,  capsule  of,  167 

endomysium  of.  168 

epimysium.  167 

fascicles  of,  167 

growth  of,  169 

intrafascicular    connective    tis- 
sue of,  168 
Muscular  system.    167 

blood-vessels  of,  169 

bursa?  of.  168 

lymphatics  of.  169 

nerves  of,  169 

technic  of,  169 

tendons  of,  16S 

tendon  sheaths  of,  168 

voluntary  muscle,  167 
tube,  128 
Muscularis   mucosa.*   of  mucous  mem- 
branes, 174 
Musculature  of  the  intestine,  92 
Myelocytes,  152 
Myeloplaxes,  153 
Myentericus,  plexus,  213 
Myocardium,  126 

Nails,  316 

cells  of  the,  31S 

development  of  the,  326 

eponychium  of  the,  318 

growth  of  the,  318 

hyponychium,  318 

lunula  of  the,  318 

structure  of  the.  316 

technic  of  the,  318 
Nares,  cells  of  the,  238 

development   of,  see   Jlevclopmciit 
of  respiratory  system 

structure  of  the.  237 

technic  of  the,  242 
Nasal  duct.  437 
Nerve  cells.  101 

amacrine,  422 

basket,  399 

bipolar,  102 

brush, 447 

caryochromes,  104 

cells  of  Betz,  404 
of  Cajal,  403 
of  Martinotti,  404 

column,  353 


INDEX. 


469 


Nerve  cells,  cone-visual,  421 
ependymal,  333 
extrinsic,  346 
ganglia,  335 

glia,  333 

Golgi  cell  type  I.,  106 

cell  type  II.,  106,  356,  404,447 
hecateromeric,  354 
heteromeric,  354 
horizontal,  422 
in  gray  matter  of  cord,  346 
intrinsic,  346 
large  granule  cells,  39S 
mitral,  447 

motor,  of  the  anterior  horn,  352 
Miiller's,  423 
multipolar,  102 
neuroblasts,  333 

of  motor  area  of  cerebral  cortex,  352 
outside  the  spinal  cord,  346,  352 
polymorphous,  405 
Purkinje,  397,  399 
pyramidal,  403 
rod-visual,  421 
root,  352 

small  granule  cells,  398 
somatochromes,  104 
spinal  ganglion,  346 
sympathetic,  332,  337 
tautomeric,  354 
technic  for,  356 
unipolar,  102 
Nerve   endings,   see   Peripheral  ne7~ve 
terminations,  348 
fibres,  medu Hated,  107 

(medullated)  of  cerebellum,  397 

association,  405 

climbing.  400 

commissural,  405 

deep  tangential,  404 

layer  of,  of  retina,  422 

motor  end-plates  of,  353 

non-medulla  ted,  108 

origin  of  fibres  of  white  matter 
of  spinal  cord,  346 

projection.  405 

rod  and  cone,  421 

superficial  tangential,  403 
terminations,  347 

motor,  353 
tissue,  1 01 


Nerve  tissue,  Golgi  methods  of  stain- 
ing, 27 
technic  for,  112 
the  neurone,  101 
Nerves,  mixed  spinal,  347 
peripheral,  338 
the  cranial,  36S 

motor  and    sensory  nuclei   of, 

368,  369 
third  (oculomotor),  395 
root  fibres  and  nucleus  of  origin 

of  third,  395 
fourth  (pathetic),  393 
fifth  (trigeminus),  374,  377 
mesencephalic  root  of  fifth,  391, 

393 
sensory  and  motor  root  fibres  of 

fifth,  3S9 
spinal   root   of   fifth,   374,   377, 

380,381,  386,    389 
sixth  (abducens),  384 
nucleus  of  origin  of  sixth,  3S4, 

3S6 
root  fibres  of  sixth,  384,  386 
seventh  (facial),  384 
nucleus   of   origin   of   seventh, 

384,  386 
root  fibres  of  seventh,  384,  386 
eighth  (auditory),  3S0,  3S1 
cochlear  branch  of  eighth,  382, 

383 
vestibular  branch  of  eighth,  383 
nuclei  of  eighth,  382,  383 
root  fibres  of  eighth,  38 1 
ninth  (glosso-pharyngeal),  374, 

378 
descending     or     sensory     root 

fibres  of  the  ninth,  374 
dorsal  nucleus  of  ninth,  37S,  3S0 
motor  nucleus  of  ninth,  378 
root  fibres  of  the  ninth.  378.  3S0 
tenth  (vagus),  374,  37S 
descending     or     sensory    root 

fibres  of  the  tenth,  374.  37S 
dorsal  nucleus  of  tenth.  37S.  380 
motor  nucleus  of  tenth.  378 
root  fibres  of  the  tenth,  378,  3S0 
eleventh  (spinal  accessory).  374 
nucleus  of   origin  of   eleventh, 

374 
root  fibres  of  eleventh.  ^74 


4/0 


INDEX. 


Nerves,  the  cranial,  twelfth  (hypoglos- 
sal), 374-  377-  38° 
nucleus    of    origin   of   twelfth, 

374-  377-  3^° 

root  of  twelfth,  3S0 

root  fibres  of  twelfth,  377 

terminal  nuclei  of.  369 
spinal,  anterior,  motor  or  efferent 
roots  of.  353 

sensory  or  afferent  portions.  347 
Nervous  system,  the.  332 

anterior  cerebral  vesicle.  332 

cerebro-spinal,  332 

development  of  (histological).  332 

forebrain.  332 

ganglia  of.  335 

hindbrain.  332 

mesencephalon.  332 

midbrain  of.  332 

middle  cerebral  vesicle,  332 

neural  fold  of,  332 

groove  of.  332 
posterior  cerebral  vesicle,  332 
prosencephalon.  332 
rhombencephalon,  332 
sympathetic,  332 
(cerebro-spinal),  the.  332 

brain,  332 

cerebellum.  397 

cerebro-spinal  axis,  332 

cerebrum,  402 

cranial  nerves,  332 

ganglia  of.  336 

isthmus,  391 

medulla  oblongata,  367 

membranes  of  brain  and  cord, 

334 

mesencephalon,  391 

midbrain,  391 

peripheral  nerves,  338 

pineal  body.  4 1 1 

pituitary      body       (hypophysis 
cerebri).  410 

spinal  cord,  332.  340 

spinal  nerves,  332 
(sympathetic),  the.  332 

ganglia,  332.  337 

origin  of,  357 

sympathetic  nerves,  332 
Neumann's  dental  sheath,  185 
Neural  fold.  332 


Neural  groove.  332 
tube.  yy 

cells  of.  333 
ependymal  cells  of,  333 
marginal  veil  of  His,  333 
neuroblasts  of,  333 
neuroglia  cells  of,  ^y 
spongioblasts  of  His,  333 
Neurilemma,  109 

and  axolemma,  relation  of,  109 
Neuroblasts,  ^y 
Neuro-epithelium,  60 
amacrine  cells,  422 
cone  bipolar  cells,  422 

visual  cells,  421 
horizontal  cells,  422 
rod  bipolar  cells,  421 
visual  cells,  421 
Neurofibrils.  103 
Neuroglia,  84,  1 1 1 
mossy  cells,  1 1 1 
Midler's  cells.  423 
neuroblasts,  1 1  1 
spider  cells,  11 1 
spongioblasts.  \  1 1 
Weigert  special  stain  for,  112 
Neurokeratin  network,  109 
Neuromuscular  bundles.  350 
Neurone,  the,  101 
axone,  106 

chromophilic  bodies,  104 
contact  theory,  j  1 1 
continuity  theory,  1  1  1 
Nissl  special  method  of  technic  for, 

104 
nucleus,  the,  102 
perifibrillar  substance.  103 
physiological  significance,  110 
protoplasmic  processes  of,  jo6 
system,  358 

afferent,  361 

corlico-spinal,  363 

efferent,  353 

No.  I.,  425 

No.  I.,  cone  neurones  of,  425 

No.  I.,  horizontal  neurones  of, 

425 
No.  I.,  rod  neurones  of,  425 
No.  II.,  426 
No.  III.,  426 
peripheral  motor,  353 


INDEX. 


471 


Neurone,   system,    peripheral    sensory, 

36:-  373 

second,  361 

spino-peripheral,  35S.  373 
the  cell  body,  ioi 
the  cytoplasm,  103 
the  dendrites,  106 
the  neurofibrils,  103 
Neurones,  cone  association,  425 

rod  association,  425 
Neutral  carmine,  15 
Neutrophile  granules,  88 
Nipple.  327 

Nissl  method  for  staining  nerve  cells, 
28 
theory,  105 
Nitric  acid  for  decalcifying,  8 
Nodes  of  Ranvier,  109 
Normoblasts,  153 
Nuclear  dyes,  13 

alum -carmine,  15 

basic  aniline,  15 

combination    of     Gage's     and 

Mayer's  formulas,  14 
Delafield's  hematoxylin,  14 
Gage's  haematpxylin,  13 
hematoxylin,  13 
Heidenhain's  hematoxylin,  14 
Alayer's  hemalum,  14 
fluid,  36 
sap,  36 

structures,  method  of  demonstrating 
by  Flemming's  fluid,  6 
Nuclein.  36 

Nucleolus  of  typical  cell,  36 
Nucleoplasm,  36 
Nucleoreticulum,  36 
Nucleus,  accessory  olivary,  374,  377,  380 
ambiguus,  378,  380 
arciform,  374,  377,  3S0.  3S1 
caudatus,  396 
Deiter's,  383 
dentate,  401 
dorsal  accessory  olivary,  37S 

cochlear,  382 
dorsalis,  361 
funiculi  cuneati,  360,  370 

gracilis,  360,  370 
lenticular,  397 

median,  of  vestibular  nerve.  3S3 
membrane  of,  36 


Nucleus,  network  of,  36 

of  acoustic  tubercle,  382 

of  a  typical  cell,  35 

of  column  of  Burdach,  360,  370 
of  Goll,  360,  370 

of  funiculus  teres,  381 

of  origin,  359 

olivary,  375,  377,  380,  381 

pre-olivary,  387 

red,  395 

semilunar,  387 

spinal  vestibular,  383 

trapezoid,  387 

ventral  cochlear.  382 

von  Bechterew's,  383 
Nuel's  space,  442 
Nutrient  canal,  155 

foramen,  155 

Odontoblasts,  1S4 

Oesophagus,  the,  191 

coats  of,  191 

glands  of,  192 

technic  of,  192 

Oil   of    origanum    cretici    for    clearing 

specimens,  18 
Olfactory  bulb,  cells  of.  447 
granule  layer,  447 
layer  of  glomeruli,  447 
layer  of  longitudinal  fibre  bun- 
dles, 447 
layer  of  mitral  cells.  447 
layer  of  olfactory  fibres,  447 
olfactory  glomeruli  of.  447 
organ, 446 

olfactory  bulb  of.  447 
olfactory  mucosa  of,  237,  446 
technic  of,  448 
Olivary  nucleus,  375,  377,  3S0,  381 
Optic  cup.  431 
nerve,  424 

arachnoid  of.  424 

dural  sheath  of,  424 

pial  sheath  of,  424 

relation    to    retina    and    brain. 

4^4 
subarachnoid  space.  424 
subdural  space.  424 
technic  of,  433 
vesicle,  431 
Ora  serrata.  420 


4/2 


INDEX. 


Oral  glands,  cells  of.  177 

crescents  of  Gianuzzi,  178 

demilunes  of  Heidenhain,  178 

mixed.  177 

mucous.  177 

serous.  177 

technic  of.  179 
Orange  G.  15 
Organ  of  Corti,  441 

cells  of  Claudius  of,  442 

Corti's  arches.  442 

Corti's  tunnel.  442 

Deiter's  cells.  442 

hair  or  auditory  cells,  442 

Hensen's  cells,  442 

lamina  reticularis  of,  443 

Nuel's  space  of,  442 

phalangeal  processes,  442 

pillar  cells  of,  441 
Organ  of  Giraldes  (paradidymis),  278 
Organ  of  Golgi.  peripheral  nerve  termi- 
nations in,  350 
Organ  of  hearing,  433 

auditory  pit  of,  444 

development  of,  444 

ear,  external,  433 

ear,  internal,  435 

ear,  middle,  434 

otic  vesicle  or  otocyst,  444 

technic  of,  445 
Organ  of  taste,  448 

cells  of,  448 

foliate  papillae,  448 

gustatory  canal,  448 

intergeminal  fibres  of,  449 

intrageminal  fibres  of.  448 

taste  buds,  182,  349,  448 

technic  of,  449 
Organ  of  vision,  412 

development  of,  431 

eyeball  or  bulbus  oculi,  412 

eyelid,    430 

lacrymal  apparatus,  429 

lens,  426 

optic  nerve,  424 
Irgans  of  special  sense,  412 

olfactory  organ,  446 

organ  of  hearing,  433 

organ  of  taste,  448 

organ  of  vision,  412 
I  Irth's  fluid.  5 


Osmic  acid  as  a  fixative,  6 

action  on  fat,  6 
on  myelin,  6 
Ossicles  of  middle  ear,  435 
Ossification  centres,  157 

endochondral.  159 

intracartilaginous,  159 

intramembranous,  157 

subperichondral,  162 

subperiosteal,  162 
Osteoblasts.  157 
Osteoclasts,  159 
Osteogenetic  tissue,  157 
Otocyst,  444 
Otolithic  membrane,  437 
Otoliths,  437 
Ovary,  288 

blood-vessels  of,  296 

epoophoron,  296 

germinal  epithelium  of,  2S8 

Graafian  follicles,  289 

lymphatics  of,  296 

nerves  of,  296 

oviduct  or  Fallopian  tube,  297 

ovum  of,  292 

paroophoron,  296 

Pfliiger's  egg  tubes  or  cords.  290 

secretion  of,  288 

structure  of,  288 

technic  of,  298 
Oviduct,  the,  297 
Ovula  Nabothi,  301 
Ovum,  39,  292 

atresia  of  follicle,  296 

development  of,  292 

maturation  of,  293 

yolk  granules  of,  293 

zona  pellucida  of,  292 

Pacchionian  bodies,  334 
Pacinian  bodies,  349 

inner  bulb  of,  350 

corpuscles,  350 
Palatine  tonsils,  see  Tonsils 
Pancreas,  the,  221 

blood-vessels  of,  226 

cell  islands  of  Langerhans,  225 

centro-acinar  cells  of  Langerhans, 
223 

development  of,  235 

duct  of  Santorini,  222 


INDEX. 


473 


Pancreas,  duct  of  Wirsung,  222 

epithelium  of  ducts,  222 

lobes  of,  221 

lobules  of,  221 

lymphatics  of,  226 

nerves  of,  226 

sustentacula!-  cells  of,  224 

technic  of,  227 

terminal  tubules  of,  222 

zymogen  granules  of,  222 
Panniculus  adiposus,  313 
Papilla;,  circumvallate,  180 

compound,  312 

filiform,  180 

fungiform,  180 

nerve,  312 

simple,  312 

vascular,  312 
Paradidymis,  or  organ  of  Giraldes,  278 
Paraffin  embedding,  11 

apparatus  for,  1 1 

sections,  staining  and  mounting  of, 

19 
Paranuclein,  36 
Paraplasm,  35 
Parathyroids,  252 

technic  of,  253 
Pareleidin,  315 
Paroophoron.  296.  309 
Parotid  gland,  218 
Parovarium,  309 
Pars  ciliaris  retinae,  417,  420 

iridica  retinae,  420 

optica  retinae.  420 
Peduncle,  inferior,  391 

middle,  391 

superior  cerebellar,  391 
Pellicula,  35 
Penicillus,  144 
Penis,  284 

arteries  of,  285 

corpora  cavernosa  of,  284 

corpus  spongiosum  of,  284 

erectile  tissue  of,  285 

glans,  2S6 

nerve  endings  of,  2S6 

prepuce  of.  2S6 

sebaceous  glands  of,  315 

technic  of,  288 

tunica  albuginea  of,  2S4 
Peptic  glands.  195 


Perforating  fibres,  152 

of  Sharpey,  152 
Periaxial  sheath,  109 
Perichondrium  of  bone,  159 

of  cartilage,  82 
Perichoroidal  lymph  spaces.  415 
Pericranium,  158 
Peridental  membrane,  187 
Perifascicular  sheath,  168,  339 
Perifibrillar  substance,  103 
Perilymph,  435 
Perimysium,  168 
Perineurium,  335,  339 
Periosteal  buds,  160 
Periosteum,  151 

Peripheral  efferent  neurone  system,  ^2 
motor  neurone  system,  353 
nerves,  338 

afferent,  347 

endoneurium  of.  339 

epineurium  of.  339 

intrafascicular    connective    tis- 
sue of,  339 

motor  or  efferent,  33S 

perifascicular  sheath  of,  339 

perineurium  of,  339 

sensory  or  afferent.  338 

technic  of,  340 
nerve  terminations,  348 

end-bulbs,  348 

free  endings,  351 

in  heart  muscle.  350 

in  mucous  membrane  of  mouth 
and  conjunctiva,  349 

in  muscle-tendon  junctions.  350 

in  skin,  348 

in  smooth  muscle.  350 

in  voluntary  muscle,  350 

muscle-tendon  organs  of  Golgi, 
350 

Pacinian  bodies.  349 

tactile  cells.  34S 

tactile  corpuscles.  348 
Perivitelline  space.  293 
Petit,  canal  of,  427 
Peyer's  patches,  204 
Pfliiger's  egg  tubes  or  cords.  290 
Phagocytes,  S8 
Phagocytosis.  SS 
Phalangeal  processes.  442 
Pharyngeal  tonsils,  see  Tonsils 


474 


IXDEX. 


Pharynx,  the,  190 

techmc  of.  190 
Pia  mater.  334 

blood-vessels  of.  235 

cerebralis.  334 

Pacchionian  bodies  of.  334 

spinalis.  341 

technic  of.  335 
Picric  acid  as  a  fixative,  6 
Picro-acid  fuchsin,  16 
Picro-carmine,  16 
Pineal  body,  411 

brain  sand  of,  411 

technic  of.  411 
Pinna.  433 
Pituitary  body,  410 

anterior  lobe  of,  410 

infundibulum  of.  411 

posterior  lobe  of,  410 

technic  of,  41 1 
Placenta.  304 

chorionic  villi  of,  304 

foetalis.  304 

technic  of,  310 

uterina.  306 
Plasma  dyes,  15 

eosin,  15 

neutral  carmine,  15 
Plasmosome,  36 
Plastids,  34 
P  las  tin.  34 

Pleuroperitoneal  cleft,  129 
Plexus  annularis,  429 

Auerbach"s,  202,  213 

Meissner's,  205,  207,  214 

myentericus,  213 
Plica.-  palmatae,  300 
Polar  bodies,  43 

Polymorphonuclear  leucocytes,  87 
Polynuclear  leucocytes,  87 
Pons  Varolii,  367,  386,  389 

longitudinal  fibres  of,  387 

pontile  nuclei  of,  387 

pyramid  of.  385 

transverse  fibres  of,  384,  387 
Posterior  columns  of   spinal   cord,  col- 
umn of  Purdach, 360 
of  spinal  cord,  column  of  Goll, 

360 
of  spinal   cord,  distribution  of 
fibres  of,  36 1 


Posterior  columns  of  spinal  cord,  origin 
of  fibres  of,  346,  351 
of  spinal  cord,  tract  or  marginal 
zone  of  Lissauer,  360 

horns,  370,  376,  378,  38 1,  3S5 

longitudinal    fasciculus,    375,    377, 
380,  3S1,  3S6,  389,  393 

medium  septum,  341 
Potassium    hydrate,   as    a    macerating 

fluid,  4 
Precapillary  artery,  119 
Prepuce,  286 
Preserving,  7 
Primary  germ  layers,  45 

renal  vesicles,  309 
Projection  fibres,  405 
Pronephros,  309 
Pronucleus,  43 
Prophase,  39 
Prosencephalon,  332 
Prostate  gland,  282 

blood-vessels  of,  283 

corpora  amylacea  of,  283 

crescentic  corpuscles  of,  283 

epithelium  of,  283 

lymphatics  of,  284 

nerves  of,  284 

technic  of,  2S4 

vesicula  prostatica,  283 
Protoplasm,  33 

theories  of  structure  of,  34 
Protoplasmic  movement,  38 

processes,  106 

radiation,  36 
Prussian   blue  gelatin,  as  an   injecting 

fluid,  20 
Purkinje  cells,  397,  399 
Pyloric  glands,  197 
Pyramidal  decussation,  362 

tracts,  362 

QUADRIGEMINA)  anterior  corpora,  391, 

3S>6 
posterior  corpora,  391,  395 

Ranvier's    alcohol,    as    macerating 

fluid,  4 
Raphe,  438 
Rectum,  the,  210 

columna.'  rectales,  210 

technic  of,  2  16 


INDEX. 


47$ 


Reissner,  membrane  of.  440 
Remak,  fibres  of,  10S 
Renal  corpuscle,  development  of,  256 
Renculus,  254 
Replacing  cells.  56 
Reproduction  of  cells.  39 
Reproductive  system,  270 
development  of,  308 
female  organs,  288 
ovary.  288 
urethra,  2S6 
uterus.  299 
vagina.  307 
male  organs.  279 

Co\vper*s  glands.  2S4 
penis,  284 
prostate  gland.  282 
testis,  270 
urethra,  286 
Respiratory  system,  development  of,  250 
the  bronchi.  242 
the  larynx.  239 
the  lungs.  244 
the  nares.  237 
the  trachea.  239 
Restiform  body,  375.  377,  3S0,  381 
Rete  testis,  tubules  of.  276 

vasa  efferentia,  276 
Reticular  formation,  371.  377,  378,  381, 

385-  389-  393 

glands.  173 

process.  342 

tissue.  73 
Retina,  the.  420 

blood-vessels  of,  428 

cells  of.  420,  421.  422.  423 

ellipsoid  of  Krause,  421 

fibre  baskets  of,  423 

fovea  centralis,  423 

ganglionic  layer.  420 

inner  limiting  membrane,  422 
molecular  layer,  421 
nuclear  layer.  421 

layer  of  nerve  cells.  422 
of  nerve  fibres.  422 
of  neuro-epithelium.  420 
of  pigmented  epithelium.  420 
of  rods  and  cones.  421 

macula  lutea,  423 

Miiller's  cells  and  fibres.  422 

ora  serrata.  420 


Retina,  outer  limiting  membrane.  420 
molecular  layer  of.  421 
nuclear  layer  of.  421 
pars  ciliaris  retinae.  420 
iridica  retinae.  42c 
optica  retinae.  420  . 
relation  to  optic  nerve.  424 
rod  and  cone  cells  of.  421 
visual  purple  of.  421 
Retzius,  lines  of,  186 
Rhombencephalon.  332 
Ribboning,  paraffin  sections.  13 
Rod  association  neurones,  425 
Rod  fibres.  421 
Rod-visual  cells.  421 
Rods,  layer  of  rods  and  cones.  421 
Rolando,  gelatinous  substance  of,  342, 

343 
Rollett's    theory   of   striated   voluntary 

muscle,  94 
Ruffini,  corpuscles  of,  325 
Rugae,  194 

Saccule,  437 

and  utricle,  437 

auditory  hairs  of.  437 
macula  acustica,  437 
neuro-epithelial  or  hair  cells  of, 

437 

otolithic  membrane  of.  437 

otoliths  of.  437 

sustentacula!-  cells  of.  437 
Safronin,  15 
Salivary  corpuscles.  141 
glands,  217 

blood-vessels  of.  219 

development  of,  235 

ducts  of.  21S 

lymphatics  of.  220 

nerves  of.  220 

parotid,  the.  218 

structure  of,  21S 

sublingual,  219 

submaxillary.  219 

technic  of.  221 

tubules  of.  21S 
Santorini.  duct  of.  235 
Sarcolemma.  92 
Sarcostyles,  169 
Scala  media.  439 
tympani.  439 


4/6 


IXDEX. 


Scala  vestibuli.  439 
Scarpa's  ganglion.  3S4 
Scheme  of  neurone  relations  of  the  spi- 
nal cord,  y^ 
Schlemm.  canal  of.  41S 
Schmidt- Lantermann  segments.  109 
Schultze.  comma  tract  of.  364 
Schwalbe.  lymph  paths  of.  428 
Schwann,  sheath  of.  109 
Sclera,  the.  412 

lamina  cribrosa  of.  412 
fusca  of.  412 
Scrotum,  skin  of.  312 
Sebaceous  glands,  315 

development  of,  327 
Sebum.  323 

Secondary  cochlear  tract.  3S4 
trigeminal  tract.  393 
vestibular  tract.  384 
Secretion.  214 
Secretory  capillaries.  Golgi  method  of 

demonstrating,  23 
Section  cutting.  12 

celloidin  specimens.  12 
paraffin  specimens.  12 
staining.  16 
Segmentation  of  ovum.  44 
Semen.  280 

Semicircular  canals,  436.  438 
crista  acustica  of,  438 
cupula  of,  438 
raphe  of,  438 
semilunar  fold  of.  438 
Seminal  ducts.  276 

epididymis.  276 
vesicles.  278 
Seminiferous  tubule.  271 
cells  of.  272 

convoluted  portion  of,  271 
spermatids,  274 
spermatocytes.  274 
spermatogones,  273 
straight  portion  of,  275 
tubules  of  the  rete  testis.  276 
Sensory  decussation,  374,  377 

peripheral  nerves.  338 
Septa  renis,  see  Kidney 
Septum  lingua-,  179 
Serial  sections.  1 3 
Sertoli,  cells  of.  272 
Sharpey's  fibres.  152 


Sheath  of  Henle,  339 

of  Schwann,  109 
Silver-nitrate  method  of  staining  inter- 
cellular substance,  23 
Skeletal  system,  articulations,  165 

bone  marrow,  152 

bones,  14S 

cartilages.  164 
Skin,  31 1 

blood-vessels  of,  324 

color  of,  315 

corpuscles  of  Meissner,  349 
of  Rufhni.  325 

derma  of,  31 1 

development  of  the,  326 

epidermis  of.  313 

Golgi-Mazzoni  corpuscles  of.  y^ 

hair  follicle  of.  319 

Krause's  end- bulbs  of,  326 

lymphatics  of,  325 

Merkel's  corpuscles  of,  348 

mitosis  of  cells  of.  315 

nerves  of,  325,  348 

of  scrotum.  312 

Pacinian  bodies  of,  349 

panniculus  adiposus  of.  313 

peripheral    nerve    terminations    in. 

34s 

prickle  cells  of,  y\ 

sebaceous  glands  of.  315 

subcutaneous  tissue  of.  312 

sweat  glands  of  (glanduhe  sudori- 
para?).  315 

sweat  pores  of.  315 

tactile  cells  of,  348 

corpuscles  of,  326,  349 

technic  of,  316 

for  blood-vessels  of.  326 

Vater-Pacinian  corpuscles  of,  325 
Skin  and  its  appendages,  31  1 

development  of.  326 

hair,  318 

mammary  gland,  327 

the  nails.  316 
Small  intestines,  200 

Auerbach's  plexus,  207 

blood-vessels  of,  211 

lirunner's  glands,  205 

cells  of,  201 

chyle  capillaries  of.  213 

coats  of,  201 


INDEX. 


477 


Small  intestines,  crypt  of  Lieberkuhn, 

-°3 

lymphatics  of,  213 

Meissner's  plexus,  205 

muscle  of,  205 

nerves  of,  213 

Peyer's  patches,  204 

te clinic  of.  216 

valvule?  conniventes  of,  200 

villi  of,  200 
Smooth  muscle  ;  see  Involuntary  muscle 
Sodium  hydrate,  as  a  macerating  fluid,  4 
Solitary  fasciculus,  374,  377,  3S0 

follicles.  19S 
Somatochromes,  104 
Spermatids.  274 
Spermatocytes.  274 
Spermatogenesis,  281 
Spermatogones.  273 
Spermatozoa,  42,  2S0 

development  of,  281 

technic  of.  2S2 
Spermatozoon,  42 
Spinal  cord,  the.  340 

anterior  column  of.  342 
horns  of,  342 
median  fissure,  341 
nerve  roots  of,  342 
white  commissure  of,  343 

antero-lateral  column  of,  342 

arachnoid  membrane  of,  334 

cell  column  of  the  lower  extremity, 

353 
column  of  the  upper  extremity, 

353 
central  canal  of,  342 

gelatinous  substance  of,  342,  343 
cervical  enlargement  of,  340 
Clarke's  column  of,  344 
column  of  Burdach,  346.  360 

of  Goll.  346,  360 
cornua  of,  342 

crossed  pyramidal  tract,  352,  362 
descending  paths  from  higher  cen- 
tres, 365 
direct    ascending   paths   to   higher 
centres.  365 

pyramidal  tract,  352.  362 

reflex  path  of,  364 
dorsal  gray  commissure  of,  3J.2 
dura  mater  of,  334 


Spinal  cord,  efferent  fibre  systems  of, 
362 
fibre  tracts  of,  358 
filum  terminale  of,  340 
fundamental  columns  of,  364 
gelatinous  substance  of  Rolando  of, 

342,  343 
gray  matter  of,  340.  342 
ground  bundles  of,  364 
indirect  ascending  paths  to  higher 
centres,  365 

reflex  paths  of,  365 
intermedio-lateral  column.  353 
lateral  column  of,  342 
longitudinal    section    of   six    days' 

chick  embryo,  357 
lumbar  enlargement  of,  340 
main  motor  fibre  systems  of.  362 
medial  column  of.  353 
medullated  fibres  of,  343.  344 
membranes  of,  334 
multipolar  ganglion  cells  of.  343 
neuroglia  cells  of.  343 

tissue  of.  342 
origin  of  fibres  of  white  matter.  346 

of  posterior  columns  of,  346 
peripheral  motor  or  efferent    neu- 
rone system,  353 
pia  mater  spinalis  of,  334.  341 
posterior  column  of,  342 

horns  of,  342 

median  septum.  341 

root  fibres  of,  342.  343 
pyramidal  tracts.  352.  362 
reticular  process  of,  342 
section    through    cervical    enlarge- 
ment of.  345 

through    lumbar    enlargement. 

34i 
through    mid-dorsal   region  of, 

344 
through  the  twelfth  dorsal  seg- 
ment. 344 
segments  of,  340 
short  fibre  systems  of.  364 
spinal  ganglion  cell.  346 
technic  of.  340.  343.  356.  366 
transverse  section  of  six  days'  chick 

embryo,  356 
ventral  gray  commissure  of.  342 
white  commissure  of.  343 


4/8 


IXDEX. 


Spinal  cord,  white  matter  of.  340,  342 

zone  of  Lissauer  of.  343 
Spinal  ganglia.  336 

development  of.  334 

technic  of.  33S 
Spinal  ganglion  cells,  ascending  arms  of 
central  processes  of.  352 

centrally  directed  arm  of.  351 

collaterals,  352 

descending   arms   of   central  proc- 
esses. 352 

development  of.  347 

ectodermic  origin  of,  346 

peripheral  arms  of,  347 

relation  to  dorsal  roots,  351 

technic  of,  356 
Spiral  ganglion,  444 

ligament,  43S 

prominence,  440 

terminations,  350 
Spireme,  39 
Spleen,  the.  142 

blood  vessels  of,  144 

cells  of,  145 

connective  tissue  of,  142 

corpuscles  of,  143 

lymphatics  of,  146 

Mall's  theory  of  vascular  channels 
of  pulp.  145 

Malpighian  bodies  of,  142 
cords  of,  144 

nerves  of.  146 

pulp  of.  144 

spindles  of,  144 

technic  of,  146 
Splenic  corpuscles,  143 

pulp,  144 
Spongioblasts  of  His,  333 
Spongioplasm,  34 
Staining,  13 

double  with  ha.-matoxylin-eosin,  16 

in  bulk.  17 

methods,  special  neurological,  25 

paraffin  sections,  19 

sections,  t6 

triple,  wilh  hematoxylin  picro- 
acid  fuchsin,  \(> 

special  methods  of.  23 
Stains,  nuclear  dyes.  13 

plasma  dyes.  13 
Stalked  hydatid.  310 


Stapes.  435 
Stomach,  the,  194 

Auerbach's  plexus,  207 

blood-vessels  of,  211 

cardiac  glands  of,  196 

chief  cells  of.  196 

development  of,  235 

epithelium  of,  194 

gastric  crypts  of,  194 
glands  of,  195 
pits  of,  194 

lymphatics  of,  213 

mucous  membrane  of,  194 

muscular  coat  of,  199 

nerves  of,  213 

parietal  cells  of,  196 

peptic  glands  of,  195 

rugae  of,  194 

secretion,  214 

solitary  follicles  of,  198 

technic  of,  199 
Stomata,  129 
Stratum  fibrosum,  165 

synovial,  166 
Stria  vascularis,  440 
Stroma  of  mucous  membranes,  174 
Styloglossal  fibres,  179 
Sublingual  gland.  219 

duct  of  Bartholin  of,  219 
Submaxillary  gland,  219 

Wharton's  duct  of,  219 
Submucosa  of  mucous  membranes,  174 
Subperichondral  ossification,  162 
Subperiosteal  ossification,  162 
Substantia  nigra,  391,  393 

propria  cornea;',  414 
Sulcus,  external  spiral,  440 
Superior  cerebellar  peduncles,  393 

olive,  387,  389 
Suspensory  ligament,  426 
Sustentacular  cells,  224 
Sweat  glands,  315 

development  of,  327 

muscle  tissue  of,  327 
Sympathetic  ganglia,  337 

development  of,  334 

technic  of,  338 
Sympathetic  nervous  system,  see  Ner- 
vous system  (sympathetic) 
Synarthrosis,  165 
Synchondrosis,  165 


INDEX. 


479 


Syncytial  tissue,  98 
Syncytium,  305 
Syndesmosis,  165 
Synovial  membrane,  166 
villi,  166 

Tactile  cells,  348 

corpuscles,  326 

of  Meissner,  349 

meniscus,  348 
Tapetum  cellulosum,  415 

fibrosum,  415 
Tarsal  glands,  430 
Tarsus,  430 

Taste  buds,  182,  349,  448 
Tautomeres,  354 
Teasing,  4 
Teeth,  the,  138 

blood-vessels  of,  187 

cementum  of,  1S6 

crown  of,  183 

dental  periosteum.  187 

dentinal  pulp  of,  183 

dentine  of,  183 

development  of,  187  ;  see  also  under 
Development  of  teelh 

enamel  of,  186 

lymphatics  of,  187 

nerves  of,  187 

Neumann's  dental  sheath,  185 

odontoblasts  of,  184 

peridental  membrane,  187 

pulp  cavity  of,  183 

root  of,  183 

technic  of,  189 
Tegmentum,  391 
Telophase,  42 
Tendon,  structure  of,  67 

sheaths,  168 
Tenon,  capsule  of,  428 
Tensor  choroideae,  418 
Terminal  nucleus,  359 
Testis,  270 

corpus    Highmori   or  mediastinum 
testis,  270 

ducts  of,  276 

epididymis  of,  271 

mediastinum,  270 

secretion  of.  280 

seminiferous  tubule  of.  271 

spermatozoa,  271 


Testis,  technic  of.  282 

tunica  albuginea  of,  270 
Theca  follicular,  289 
Thionin,  15 

Thoma,  ampullae  of,  146 
Thrombocytes,  88 
Thymus,  the,  138 

blood-vessels  of,  139 

development  of,  138 

Hassal's  corpuscles,  139 

lymphatics  of,  139 

nerves  of,  139 

structure  of,  138 

technic  of,  139 
Thyroid,  251 

blood  supply  of,  252 

colloid  of,  251 

development  of,  252 

isthmus  of,  251 

lymphatics  of,  252 

nerves  of,  252 

structure  of,  251 

technic  of,  253 
Tissue  elements,  dissociation  of,  4 
Tissues,  49 

adipose,  75 

blood,  85 

bone,  82 

cartilage,  79 

classification  of,  51 

connective,  63 

epithelial,  53 

erectile,  285 

examination  of  fresh,  4 

histogenesis  of,  51 

lymphatic,  75 

muscle,  91 

nerve,  101 

osteogenetic.  157 

subcutaneous,  312 
Toluidin  blue,  15 
Tomes'  process,  189 
Tongue,  the,  179 

blood-vessels  of,  181 

circumvallate  papilla-,  1S0 

connective  tissue  of.  179 

Ebner's  glands,  1S2 

end-bulbs  of  Krause.  1S2 

filiform  papilla?,  180 

fungiform  papillae,  1S0 

glands  of.  1S1 


480 


INDEX. 


Tongue,  longitudinal  fibres  of.  179 

lymph  follicles  of,  141,  1S1 
spaces,  1S2 

muscles  of,  179 

nerves  of,  1S2 

septum  linguae.  179 

taste  buds.  1S2 

technic  of.  1S2 

transverse  fibres  of,  179 

vertical  fibres  of.  179 
Tonsils,  the,  140 

blood-vessels  of,  142 

crypts  of,  140 

development  of.  142 

lingual:  follicuii  linguales,  141 

lymphatics  of,  142 

nerves  of,  142 

palatine  or  true,  140 

pharyngeal  tonsils,  142 

salivary  corpuscles  of,  141 

structure  of.  140 

technic  of.  142 
Trachea,  239 

cartilages  of  the,  240 

structure  of  the,  239 

technic  of  the,  242 
Tract  of  Flechsig,  361 
Transitional  leucocytes,  87 
Trapezium,  387 
Tunica  albuginea,  284 

dartos.  312 

propria,  of  mucous  membranes,  174 

vaginalis.  270 
Tympanic  membrane,  434 
Tympanum.  434;  see  also  Ear,  middle 
Tyson,  glands  of,  286 

Ultimate  fihkilLjE,  93 

I  'nipolar  nerve  cells,  102 
Ureter,  264 

technic  of,  269 
Urethra,  male,  286 

blood-vessels  of,  287 
fossa  navicularis,  287 
glands  of,  287 
structure  of,  286 
technic  of,  288 
Urinary  bladder,  265 
epithelium  of,  265 
Urinary  system,  254 
adrenal,  266 


Urinary  system,  development  of,  308 

kidney,  254 

kidney-pelvis,  264 

ureter,  264 

urinary  bladder,  265 
Uriniferous  tubule,  256 

arched  tubule  of,  260 

ascending  arm  of  Henle's  loop,  259 

descending  arm  of  Henle's  loop,  259 

epithelium  of,  260 

first  on  proximal  convoluted  tubule 
of,  259 

Henle's  loop  of,  259 

Malpighian  body,  25S 

neck  of,  259 

second  or  distal  convoluted  tubule, 

259 
straight  or  collecting  tubule  of,  260 
Uterus,  blood-vessels  of,  306 
decidual  cells  of,  303 
development  of,  308;  see  also  De- 
velop meat  of  reproductive  system 
lymphatics  of,  307 
masculinus,  283 
muscle  tissue  of,  299 
nerves  of,  307 
placenta,  304 

mucosa  of  menstruating,  301 
of  pregnant,  303 
of  resting,  300 
stage  of  menstruation  proper,  302 
of  preparation,  301 
of  reparation,  302 
structure  of,  299 
technic  of,  310 

with  placenta   in   situ,  technic  of, 
310 
Utricle,    437 ;     see    also    Saccule    and 

Utricle 
Utriculosaccular  duct,  436 
Utriculus  prostaticus,  283 

Vagina,  307 

blood-vessels  of,  308 

nerves  of,  308 

technic  of,  310 
Valvulae  conniventes,  200 
Vas  deferens,  277 

ampulla  of,  278 

technic  of,  282 
Vas  epididymis,  277 


INDEX. 


48  1 


Vasa  efferentia,  277 

vasorum,  124 
Vascular  papillae,  312 
Vascular  system,  see  Circulatory  system 
Vater-Pacinian  corpuscles.  325 
Veins,  122 

adventitia  of,  124 

central,  229 

coats  of,  122 

development  of,  128 

intima  of,  123 

media  of,  123 

portal,  229 

stellate,  of  Verheyn,  263 

technic  of,  124 

vasa  vasorum,  124 

venae  vorticosae,  415 
Venae  vorticosae,  415 
Ventricle,  fourth,  378,  380,  386,  389 
Verheyn,  stellate  veins  of.  263 
Vermiform  appendix.  208 

lymph  nodules  of.  210 

technic  of.  216 
Vesicle,  anterior  cerebral.  332 

middle  cerebral.  332 

optic.  431 

otic,  444 

posterior  cerebral.  332 
Vesicula  prostatica,  283 
Vestibular  ganglion,  384 
Vestibule,  308,  436 

ductus  reuniens  of.  436 

endolymphatic  duct.  436 

saccule  of,  436.  437 

utricle  of.  436,  437 

utriculo  saccular  duct  of,  436 
Vieussens,  valve  of.  391 
Villi,  201 

Visual  purple,  421 
Vitreous  body,  427 

Cloquet's  canal,  427 

hyaloid  canal  of,  427 
Vitreous  membrane  of  choroid,  416 


Vocal  cords,  the,  239 
Volkmanivs  canal.  151 
Voluntary  striated  muscle,  92 

Cohnheim*s  held.  94 

end-bulbs  of.  350 

Hensen's  line.  93 

Krause's  line,  93 

muscle  columns  of  Kolliker,  94 
discs,  93 
spindles  of.  350 

nerves  of,  350 

Pacinian  corpuscles  of,  350 

Rollett's  theory,  94 

sarcolemma,  92 

technic  of,  100 

white  and  red  fibres,  95 
Von  Bechterew's  nucleus,  383 
Von  Monakow,  tract  or  bundle  of,  363, 
37°.  376,  378.  3s*  •  3841  389.  393 

Weigert's  elastic-tissue  stain,  23 
method  of  staining  medullated  nerve 
fibres,  26 

Weigert  Pal  method,  26 

Wirsung,  duct  of.  222 

Wolffian  bodies.  309 
ridge.  309 

Xylol,  and  cajeput  oil  for  clearing,  18 
-paraffin  for  embedding.  11 

Zenker's  fluid,  for  decalcifying,  8 

for  fixation,  6 
Zinn,  zonule  of,  426 
Zona  pectinata,  441 

pellucida,  292 

tecta,  441 
Zone  of  Lissauer,  343 

of  oval  nuclei,  238 

of  round  nuclei,  238 
Zonula  ciliaris,  426 
Zonule  of  Zinn,  426 
Zymogen  granules,  222 


8 1 s" 


a  n  s-s-( 


8  b' 


COLUMBIA  UNIVERSITY  LIBRARIES 


0041079361 


